It improves readability of code and reduces the chance to make a mistake.

This patch also fixes a bug with nan-boxing builds by rounding up the
calculation of the new NSLOTS variable, giving the correct number of slots
(being 4) even if mp_obj_t is larger than the native machine size.

These values are used to compute memory addresses and so size_t is the
more appropriate type to use.

This assures after cleaning all build artefacts (qstr related files,
generated version header) have been removed.

Instead of having the PlatformToolset property hardcoded to a specific
version just set it to the value of DefaultPlatformToolset: this gets
defined according to the commandline environment in which the build was
started.
Instead of just supporting VS2015 the project can now be built by any
version from VS2013 to VS2017 and normally future versions as well, without
quirks like VS asking whether you want to upgrade the project to the latest
version (as was the case when opening the project in VS2017) or not being
able to build at all (as was the case when opening the project in VS2013).

Also adjust the .gitignore file to ignore any artefacts from VS2017.

The -ansi flag is used for C dialect selection and it is equivalent to -std=c90.
Because it goes right before -std=gnu99 it is ignored as for conflicting flags
GCC always uses the last one.

Now, passing a keyword argument that is not expected will correctly report
that fact.  If normal or detailed error messages are enabled then the name
of the unexpected argument will be reported.

This patch decreases the code size of bare-arm and stmhal by 12 bytes, and
cc3200 by 8 bytes.  Other ports (minimal, unix, esp8266) remain the same in
code size.  For terse error message configuration this is because the new
message is shorter than the old one.  For normal (and detailed) error
message configuration this is because the new error message already exists
in py/objnamedtuple.c so there's no extra space in ROM needed for the
string.

GIL behaviour should be handled by the port.  And ports probably want to
define sleep_us so that it doesn't release the GIL, to improve timing
accuracy.

When locking/unlocking a mutex we only need to protect against a thread
switch, not general interrupts.

This way, Timer and ExtInt callbacks can interrupt the low-priority
pendsv handler (for example thread switching).

Thanks to @robert-hh.

We can actually handle interrupts during a thread switch (because we always
have a valid stack), but only if those interrupts don't access any of the
thread state (because the state may not correspond to the stack pointer).
So to be on the safe side we disable interrupts during the very short
period of the thread state+stack switch.

The scheduler being locked general means we are running a scheduled
function, and switching to another thread violates that, so don't switch in
such a case (even though we technically could).

And if we are running a scheduled function then we want to finish it ASAP,
so we shouldn't switch to another thread.

Furthermore, ports with threading enabled will lock the scheduler during a
hard IRQ, and this patch to the VM will make sure that threads are not
switched during a hard IRQ (which would crash the VM).

MHLSB and MHMSB formats are added to the framebuf module, which have 8
adjacent horizontal pixels represented in a single byte.

Since eaef6b53 writes are used instead of
reads.

All arguments to pin.irq are converted from keyword-only to positional, and
can still be specified by keyword so it's a backwards compatible change.

The default value for the "trigger" arg is changed from 0 (no trigger)
to rising+falling edge.

ExtInt, Timer and CAN IRQ callbacks are made to work with the scheduler.
They are still hard IRQs by default, but one can now call
micropython.schedule within the hard IRQ to schedule a soft callback.

Instead of always reporting some object cannot be implicitly be converted
to a 'str', even when it is a 'bytes' object, adjust the logic so that
when trying to convert str to bytes it is shown like that.
This will still report bad implicit conversion from e.g. 'int to bytes'
as 'int to str' but it will not result in the confusing
'can't convert 'str' object to str implicitly' anymore for calls like
b'somestring'.count('a').

* Fix mis-spelling of `ticks_add` in code examples.
* Be consistent about parentheses after function names.
* Be consistent about formatting of function, variable and constant names.
* Be consistent about spaces and punctuation.
* Fix some language errors (missing or wrong words, wrong word order).
* Keep line length under 90 chars.

Signed-off-by: Christopher Arndt <chris@chrisarndt.de>

This has a noticeable improvement on x86-64 and Thumb2 archs, where stack
usage is reduced by 2 machine words in the VM.

Instead of caching data that is constant (code_info, const_table and
n_state), store just a pointer to the underlying function object from which
this data can be derived.

This helps reduce stack usage for the case when the mp_code_state_t
structure is stored on the stack, as well as heap usage when it's stored
on the heap.

The downside is that the VM becomes a little more complex because it now
needs to derive the data from the underlying function object.  But this
doesn't impact the performance by much (if at all) because most of the
decoding of data is done outside the main opcode loop.  Measurements using
pystone show that little to no performance is lost.

This patch also fixes a nasty bug whereby the bytecode can be reclaimed by
the GC during execution.  With this patch there is always a pointer to the
function object held by the VM during execution, since it's stored in the
mp_code_state_t structure.

The RHS can only be returned if it is the same type as the LHS.

This allows to test the PYBV11 target as well as the network drivers
without adding another rule.  It also removes the need to use -B,
side-stepping the issue of whether or not -B works with qstr auto
generation.

When make is passed "-B" it seems that everything is considered out-of-date
and so $? expands to all prerequisites.  Thus there is no need for a
special check to see if $? is emtpy.