ir_irmp: Python binding, support instance locking and context manager

ir_irmp: Python binding, support instance locking and context manager

Extend the ctypes wrapper for the IRMP decoder core. Add routines for
the instance state creation and lock management. Implement metamethods
for Python context managers which lock the instance to protect the C
library's internal state from changing unexpectedly. Add my copyright
for the non-trivial changes.

This commit eliminates the limitation to a single IRMP decoder core for
the sigrok process to use. Multiple Python callers can synchronize their
library use, and see a consistent library state across the scope of the
context manager. It's essential though that callers leave the context
to not block other callers for extended periods of time.