No need to call DECODE_UINT since the value will always be either 2 or 3.

When obj.h is compiled as C++ code, the cl compiler emits a warning about
possibly unsafe mixing of size_t and bool types in the or operation in
MP_OBJ_FUN_MAKE_SIG.  Similarly there's an implicit narrowing integer
conversion in runtime.h.  This commit fixes this by being explicit.

This is an improvement over previous behavior when str was returned for
both str and bytes input format.  This new behaviour is also consistent
with how the % operator works, as well as many other str/bytes methods.

It should be noted that it's not how current versions of CPython work,
where there's a gap in the functionality and bytes.format() is not
supported.

This will allow to e.g. implement HTTP Digest authentication.

Adds 540 bytes for x86_32, 332 for arm_thumb2 (for Unix port, which already
includes axTLS library).

This commit adds the math.factorial function in two variants:
- squared difference, which is faster than the naive version, relatively
  compact, and non-recursive;
- a mildly optimised recursive version, faster than the above one.

There are some more optimisations that could be done, but they tend to take
more code, and more storage space.  The recursive version seems like a
sensible compromise.

The new function is disabled by default, and uses the non-optimised version
by default if it is enabled.  The options are MICROPY_PY_MATH_FACTORIAL
and MICROPY_OPT_MATH_FACTORIAL.

The CDC maximum packet size is 512 bytes, or 128 32-bit words, and the TX
FIFO must be configured to have at least this size.

Configuring clocks is a critical operation and is best to avoid when
possible.  If the clocks really need to be reset to the same values then
one can pass in a slightly higher value, eg 168000001 Hz to get 168MHz.

This ensures that on first boot the most optimal settings are used for the
voltage scaling and flash latency (for F7 MCUs).

This commit also provides more fine-grained control for the flash latency
settings.

APB1/APB2 are derived from AHB, so if the user sets AHB!=SYSCLK then the
APB1/APB2 dividers must be computed from the new AHB.

Power and clock control is low-level functionality and it makes sense to
have it in a dedicated file, at least so it can be reused by other parts of
the code.

On F7s PLLSAI is used as a 48MHz clock source if the main PLL cannot
provide such a frequency, and on L4s PLLSAI1 is always used as a clock
source for the peripherals.  This commit makes sure these PLLs are
re-enabled upon waking from stop mode so the peripherals work.

See issues #4022 and #4178 (L4 specific).

There appears to be an issue on Windows with CPython >= 3.6,
sys.stdout.flush() raises an exception:

    OSError: [WinError 87] The parameter is incorrect

It works fine to just catch and ignore the error on the flush line.  Tested
on Windows 10 x64 1803 (Build 17134.228), Python 3.6.4 amd64.

They need time (around 4us for VREFINT) to obtain accurate results.

Fixes issue #4022.

This patches avoids multiplying with negative powers-of-10 when parsing
floating-point values, when those powers-of-10 can be exactly represented
as a positive power.  When represented as a positive power and used to
divide, the resulting float will not have any rounding errors.

The issue is that mp_parse_num_decimal will sometimes not give the closest
floating representation of the input string.  Eg for "0.3", which can't be
represented exactly in floating point, mp_parse_num_decimal gives a
slightly high (by 1LSB) result.  This is because it computes the answer as
3 * 0.1, and since 0.1 also can't be represented exactly, multiplying by 3
multiplies up the rounding error in the 0.1.  Computing it as 3 / 10, as
now done by the change in this commit, gives an answer which is as close to
the true value of "0.3" as possible.

This is required for DEBUG=1 builds when MICROPY_FLOAT_IMPL=double.

Thanks to Andrew Leech.

This provides a double variant of the float copysignf from libm/math.c
which is required for DEBUG=1 builds when MICROPY_FLOAT_IMPL=double

pyb.mount(None, mountpoint) functionality is also removed and replaced by
uos.umount.

pyb.umount(None, mountpoint) no longer works.

Changes made:
- make use of MP_OBJ_TO_PTR and MP_OBJ_FROM_PTR where necessary
- fix shadowing of index variable i, renamed to j
- fix type of above variable to size_t to prevent comparison warning
- fix shadowing of res variable
- use "(void)" instead of "()" for functions that take no arguments

And thus be buildable again.

This commit implements PEP479 which disallows raising StopIteration inside
a generator to signal that it should be finished.  Instead, the generator
should simply return when it is complete.

See https://www.python.org/dev/peps/pep-0479/ for details.

This part is functionally similar to STM32F767xx (they share a datasheet)
so support is generally comparable.  When adding board support the
stm32f767_af.csv and stm32f767.ld should be used.

Instead of redirecting to str.__mod__(), use str.format() in this case.

Default is enabled, disabled for minimal builds. Saves 1296 bytes on x86,
976 bytes on ARM.

In 0e80f345 the inplace operations __iadd__
and __isub__ were made unconditionally available, so the comment about this
section is changed to reflect that.