Refactored from "stm" module, provides mem8, mem16, mem32 objects with
array subscript syntax.

Previous to this patch the printing mechanism was a bit of a tangled
mess.  This patch attempts to consolidate printing into one interface.

All (non-debug) printing now uses the mp_print* family of functions,
mainly mp_printf.  All these functions take an mp_print_t structure as
their first argument, and this structure defines the printing backend
through the "print_strn" function of said structure.

Printing from the uPy core can reach the platform-defined print code via
two paths: either through mp_sys_stdout_obj (defined pert port) in
conjunction with mp_stream_write; or through the mp_plat_print structure
which uses the MP_PLAT_PRINT_STRN macro to define how string are printed
on the platform.  The former is only used when MICROPY_PY_IO is defined.

With this new scheme printing is generally more efficient (less layers
to go through, less arguments to pass), and, given an mp_print_t*
structure, one can call mp_print_str for efficiency instead of
mp_printf("%s", ...).  Code size is also reduced by around 200 bytes on
Thumb2 archs.

This simplifies the API for objects and reduces code size (by around 400
bytes on Thumb2, and around 2k on x86).  Performance impact was measured
with Pystone score, but change was barely noticeable.

Given that there's already support for "fixed table" maps, which are
essentially ordered maps, the implementation of OrderedDict just extends
"fixed table" maps by adding an "is ordered" flag and add/remove
operations, and reuses 95% of objdict code, just making methods tolerant
to both dict and OrderedDict.

Some things are missing so far, like CPython-compatible repr and comparison.

OrderedDict is Disabled by default; enabled on unix and stmhal ports.

See issue #699.

See issue #699.

This patch consolidates all global variables in py/ core into one place,
in a global structure.  Root pointers are all located together to make
GC tracing easier and more efficient.

Addresses issue #1022.

This patch adds a configuration option (MICROPY_CAN_OVERRIDE_BUILTINS)
which, when enabled, allows to override all names within the builtins
module.  A builtins override dict is created the first time the user
assigns to a name in the builtins model, and then that dict is searched
first on subsequent lookups.  Note that this implementation doesn't
allow deleting of names.

This patch also does some refactoring of builtins code, creating the
modbuiltins.c file.

Addresses issue #959.

For this, introduce MICROPY_MODULE_DICT_SIZE config setting.

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.

Specifically, nlr.h does.

At this point, all opcodes are now implemented!

Some del opcodes have been combined with store opcodes, with the value
to store being MP_OBJ_NULL.

Finishes addressing issue #424.

In the end this was a very neat refactor that now makes things a lot
more consistent across the py code base.  It allowed some
simplifications in certain places, now that everything is a dict object.

Also converted builtins tables to dictionaries.  This will be useful
when we need to turn builtins into a proper module.

Towards addressing issue #424.

Had a small increase to ROM usage (order 60 bytes).

Pretty much everyone needs to include map.h, since it's such an integral
part of the Micro Python object implementation.  Thus, the definitions
are now in obj.h instead.  map.h is removed.

Comes with some refactoring of code and renaming of files.  All modules
are now named mod*.[ch].

* Add function to load static modules.
* Use module_register to pyb module.

Remove unnecessary includes. Add includes that improve portability.

mp_module_obj_t can now be put in ROM.

Configuration of float type is now similar to longint: can now choose
none, float or double as the implementation.

math module has basic math functions.  For STM port, these are not yet
implemented (they are just stub functions).

Each built-in exception is now a type, with base type BaseException.
C exceptions are created by passing a pointer to the exception type to
make an instance of.  When raising an exception from the VM, an
instance is created automatically if an exception type is raised (as
opposed to an exception instance).

Exception matching (RT_BINARY_OP_EXCEPTION_MATCH) is now proper.

Handling of parse error changed to match new exceptions.

mp_const_type renamed to mp_type_type for consistency.

Ultimately all static strings should be qstr.  This entry in the type
structure is only used for printing error messages (to tell the type of
the bad argument), and printing objects that don't supply a .print method.

Some tools do not support local/static symbols (one example is GNU ld map file).
Exposing all functions will allow to do detailed size comparisons, etc.

Also, added bunch of statics where they were missing, and replaced few identity
functions with global mp_identity().

STM port crashes without this re-init.  There should not be any state in
the core py/ code that relies on pre-initialised data.

Can now have null bytes in strings.  Can define ROM qstrs per port using
qstrdefsport.h

In Python, importing module several times returns same underlying module
object. This also fixes import statement handling for builtin modules.

There're still issues:
1. CPython exposes set of loaded modules as sys.modules, we may want to
do that either.
2. Builtin modules are implicitly imported, which is not really correct.
We should separate registering a (builtin) module and importing a module.
CPython keeps builtin module names in sys.builtin_module_names .

Change state layout in VM so the stack starts at state[0] and grows
upwards.  Locals are at the top end of the state and number downwards.
This cleans up a lot of the interface connecting the VM to C: now all
functions that take an array of Micro Python objects are in order (ie no
longer in reverse).

Also clean up C API with keyword arguments (call_n and call_n_kw
replaced with single call method that takes keyword arguments).  And now
make_new takes keyword arguments.

emitnative.c has not yet been changed to comply with the new order of
stack layout.

Creating of classes (types) and instances is much more like CPython now.
You can use "type('name', (), {...})" to create classes.

It's not really about that, though; it's about me figuring out a sane
way forward for keyword-argument functions (and function
metadata). But it's useful as is, and shouldn't break any existing
code, so here you have it; I'm going to park it in my mind for a bit
while sorting out the rest of the dict branch.