So corresponding exception can be thrown even under tight memory conditions.

Traceback allocation for exception will now never lead to recursive
MemoryError exception - if there's no memory for traceback, it simply
won't be created.

They are directly cast to str object, skipping allocation of formatting
buffer.

Has to be enabled by manual editing, but at least it's there, as debugging
NLR issues may be weird.

Pushing same NLR record twice would lead to "infinite loop" in nlr_jump
(but more realistically, it will crash as soon as NLR record on stack is
overwritten).

Conceptually it is part of code state, so let it be allocated in the same way
as the rest of state.

Addresses issue #1117.

Addresses issue #1119.

Now all ports can use pybstdio.c to provide sys.stdin/stdout/stderr, so
long as they implement mp_hal_stdin_* and mp_hal_stdout_* functions.

Apparently the order of interface numbers should be sequential and
increasing in a config descriptor.  So as to retain compatibility with
Windows drivers for the CDC+MSC and CDC+HID modes, we move the CDC
configs to the end of the descriptors, instead of changing the interface
numbers.

See PR #957 for background.

Different HID modes can be configured in Python.  You can either use
predefined mouse or keyboard, or write your own report descriptor.

The unused files are from the ST demos for different USB classes and are
not needed for the stmhal port.

Addresses issue #1113.

Also gives line number of location of error.  Very useful!

These are useful for implementing atomic lock operations.