This adds a newu mmap module to the unix port. This is modeled after the
standard mmap module and just contains minimal functionality to read and
write to a mmap.

This provides the ioctl function similar to the Python standard library

Since we use graphics mode, text printed to stdout it not visible on
the EV3 when running with brickrun. The ev3dev VS Code extension
redirects stderr to the output pane, but not stdout. So we redirect
stdout to stderr by default so that print() "just works".

When we run this test in the ev3dev-stretch/armel docker container,
it fails because the 64-bit host python is used to generated the .exp
file but the test is run using 32-bit ARM emulation which results in
different sizes.

Images can use quite a bit of memory so we are running out of heap
space. This increases the heap from 1M to 8M which is 1/4 of the total
RAM on the EV3.

This adds a workaround for tests/basics/stopiteration.py on Python 3.5.

It appears that Python fixed a bug after Python 3.5 that changed the
behavior. Since Python 3.5 is no longer supported, it doesn't make
sense to upstream a workaround. So we just add a hack for ev3dev-stretch.

This is causing intermittent CI failures. In fact, it was disabled
upstream in the past [1]. We don't support threading anyway, so we
can ignore it as well.

[1]: 567e7fc

The ubinascii_b2a_base64 test fails on ev3dev-stretch since it requires
a Python 3.6 feature and ev3dev-stretch is stuck with Python 3.5.

This uses MP_STATE_IS_MAIN_THREAD macro to ensure that the scheduler
only runs on the main thread. This is similar to the way CPython only
allows pending calls on the main thread (ref: Py_AddPendingCall).

This adds a new mp_thread_schedule_exception() function that performs
the same function as PyThreadState_SetAsyncExc() in CPython.

This is useful as a mechanism for cancelling/interrupting threads.

https://docs.python.org/3/c-api/init.html#c.PyThreadState_SetAsyncExc

This adds a new `MICROPY_VARIANT_QSTR_DEFS_H` option to allow variants
to add additional qstrs to the unix port.

Signed-off-by: David Lechner <david@pybricks.com>

This adds a new, optional mp_hal_stdout_tx_flush() function and uses
it to implement the `flush()` method for `sys.stdout`.

We need some fixes not relevant to MicroPython so we have to use our
own fork now.

Change math and cmath module registration from normal to extensible.
This lets the fallback umath and ucmath names work when importing.

Add a case to handle 'i' in addition to 'd' in mp_vprintf().

There are some 3rd-party libraries that use 'i' in format strings, so
it is useful to support this.

Signed-off-by: David Lechner <david@pybricks.com>