Before this patch:

    >>> print(')
    ... ')
    Traceback (most recent call last):
      File "<stdin>", line 1
    SyntaxError: invalid syntax

After this patch:

    >>> print(')
    Traceback (most recent call last):
      File "<stdin>", line 1
    SyntaxError: invalid syntax

This matches CPython and prevents getting stuck in REPL continuation when a
1-quote is unmatched.

Before this patch, when using the switch statement for dispatch in the VM
(not computed goto) a pending exception check was done after each opcode.
This is not necessary and this patch makes the pending exception check only
happen when explicitly requested by certain opcodes, like jump.  This
improves performance of the VM by about 2.5% when using the switch.

I2C costs about 3000 bytes of code, and SPI costs about 4400 bytes.

This matches CPython behaviour on Linux: a socket that is new and not
listening or connected is considered "hung up".

Thanks to @rkojedzinszky for the initial patch, PR #3457.

Instead of crashing due to out-of-bounds array access.  Fixes #3348.

Instead of crashing due to NULL pointer dereference.  Fixes issue #3341.

To make it easier/simpler to write code that can run under both CPython and
on an ESP8266 board.

lwIP v2.0.3 has been tested with this lwip module and it works very well.

This patch fixes the macro so you can pass any name in, and the macro will
make more sense if you're reading it on its own.  It worked previously
because n_state is always passed in as n_state_out_var.

Having balanced braces { and } makes it easier to navigate the function.

WIFI_MODE_NULL is no longer supported by the ESP IDF, instead one must use
esp_wifi_start/esp_wifi_stop.

gcc 8.0 supports the naked attribute for x86 systems so it can now be used
here.  And in fact it is necessary to use this for nlr_push because gcc 8.0
no longer generates a prelude for this function (even without the naked
attribute).

Some compilers cannot deduce that cdc will always be written before being
used.

This patch adds the configuration MICROPY_HW_USB_ENABLE_CDC2 which enables
a new USB device configuration at runtime: VCP+VCP+MSC.  It will give two
independent VCP interfaces available via pyb.USB_VCP(0) and pyb.USB_VCP(1).
The first one is the usual one and has the REPL on it.  The second one is
available for general use.

This configuration is disabled by default because if the mode is not used
then it takes up about 2200 bytes of RAM.  Also, F4 MCUs can't support this
mode on their USB FS peripheral (eg PYBv1.x) because they don't have enough
endpoints.  The USB HS peripheral of an F4 supports it, as well as both the
USB FS and USB HS peripherals of F7 MCUs.

The documentation (including the examples) for elapsed_millis and
elapsed_micros can be found in docs/library/pyb.rst so doesn't need to be
written in full in the source code.

When disabled, the pyb.I2C class saves around 8k of code space and 172
bytes of RAM.  The same functionality is now available in machine.I2C
(for F4 and F7 MCUs).

It is still enabled by default.

This is enabled by default.  When it is disabled all legacy functions and
classes in the pyb module are excluded from the build.

And remove the old one based on ST code.

This driver uses low-level register access to control the I2C peripheral
(ie it doesn't rely on the ST HAL) and provides the same C-level API as the
existing F7 hardware driver.

The USB IRQ may fire once USBD_HID_ClearNAK() is called and then change the
last_read_len value.

USB_HID.send() should now return 0 if it could not send the report to the
host.

- Updated supported git hash to current IDF version.
- Added missing targets and includes to Makefile.
- Updated error codes for networking module.
- Added required constant to sdkconfig configuration.

This patch moves the start of the root pointer section in mp_state_ctx_t
so that it skips entries that are not pointers and don't need scanning.

Previously, the start of the root pointer section was at the very beginning
of the mp_state_ctx_t struct (which is the beginning of mp_state_thread_t).
This was the original assembler version of the NLR code was hard-coded to
have the nlr_top pointer at the start of this state structure.  But now
that the NLR code is partially written in C there is no longer this
restriction on the location of nlr_top (and a comment to this effect has
been removed in this patch).

So now the root pointer section starts part way through the
mp_state_thread_t structure, after the entries which are not root pointers.

This patch also moves the non-pointer entries for MICROPY_ENABLE_SCHEDULER
outside the root pointer section.

Moving non-pointer entries out of the root pointer section helps to make
the GC more precise and should help to prevent some cases of collectable
garbage being kept.

This patch also has a measurable improvement in performance of the
pystone.py benchmark: on unix x86-64 and stm32 there was an improvement of
roughly 0.6% (tested with both gcc 7.3 and gcc 8.1).

Also remove trailing whitespace and convert tabs to spaces.

This patch is only cosmetic and has no functional change.

This patch changes 2 things in the endianness detection:

1. Don't assume that __BYTE_ORDER__ not being __ORDER_LITTLE_ENDIAN__ means
   that the machine is big endian, so add an explicit check that this macro
   is indeed __ORDER_BIG_ENDIAN__ (same with __BYTE_ORDER, __LITTLE_ENDIAN
   and __BIG_ENDIAN).  A machine could have PDP endianness.

2. Remove the checks which base their autodetection decision on whether any
   little or big endian macros are defined (eg __LITTLE_ENDIAN__ or
   __BIG_ENDIAN__).  Just because a system defines these does not mean it
   has that endianness.

See issue #3760.

These special methods are all available if MICROPY_PY_ALL_SPECIAL_METHODS
is enabled.