collections.deque: Add support of len().
collections.deque: Add support of __bool__().

To support `if deque_inst` and similar.
collections.deque: Optimize __bool__().
collecions.deque: Release 0.1.1.
select: Clarify comment.
uasyncio.core: Doesn't depend on heapq module for some time now.
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.