Byte code has a map from byte-code offset to source-code line number,
used to give better error messages.

Now searches both locals_dict and methods.  Partly addresses Issue #145.

Now working for class-defined methods: __getitem__, __setitem__,
__add__, __sub__.  Easy to add others.

mp_obj_int_get() can be used when just full resolution of C machine_int_t
is required (returns truncated value of long int). mp_obj_int_get_checked()
will throw exception if Python int value not representable in machine_int_t.

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.

Implicit "micropython" module contains (at least) codegeneration decorators.
Make it explicit, so an app could have "import micropython". On MicroPython,
that will be no-op. On CPython, that will give a chance to have a module
with placeholder decorators.

Per Python3 io module semantics.

That at least makes stuff like "{:x}".format(1) to produce not completely
broken output.

Parser no longer prints an error, but instead returns an exception ID
and message.

So far, don't work for strings as expected.

This implements internal args tuple of arguments, while still keeping
object useful for reporting C-side errors.

Further elaboration is needed.

This is useful because tuple is closest analog of C static array.

vstr is initially intended to deal with arbitrary-length strings. By
providing a bit lower-level API calls, it will be also useful to deal
with arbitrary-length I/O buffers (the difference from strings is that
buffers are filled from "outside", via I/O).

Another issue, especially aggravated by I/O buffer use, is alloc size
vs actual size length. If allocated 1Mb for buffer, but actually
read 1 byte, we don't want to keep rest of 1Mb be locked by this I/O
result, but rather return it to heap ASAP ("shrink" buffer before passing
it to qstr_from_str_take()).

By dispatching to long int methods.

Made sorted() raise an exception instead of aborting when given no arguments; moved around some things in objfun.c as a consequence