runtime: configuring loggers in gr Python module for easy use in Python.

Can use gr.log.<level>('log message') or gr.log_debug directly from python to output logging info based on the [LOG] preferences.
fec: use logger to explain exception when using threading with history.
blocks: add optional argument to deinterleave and interleave ctors to not set relative rate.

Whe using blocks of data, this doesn't always make sense (see the threading of the extended encoder and decoder in gr-fec).
fec: wip: adding a dummy encoder/decoder to exercise the API.
fec: wip: adding a simple repetition code as another example.
fec: wip: cleaning up; examples