uasyncio.queues: Add simple implementation of asynchronous queues for uasyncio
select: Clarify comment.
os: check_error(): Return true for EINTR, to easily restart system calls.
select: Handle EINTR.
fcntl: Implement fcntl/ioctl variants which take memory buffer as arg.
fcntl: fcntl/ioctl arg defaults to 0 per CPython.
fcntl: Add error checking and at least TODOs about buffer return values.
signal: Add basic signal implementation (only IGN & DFL are supported).
signal: Add test for SIG_IGN functionality.
signal: Implement support for Python handlers.
signal: Add example of signal handler in Python.