adding a concrete example of config file in config.json

It contains mappings for Corsair Vengeance K70 multimedia keys in my
particular system (controls for mocp)
adding some tests to time management in keylog_parser.py
correcting a bug in parse_buffer() coroutine

When user wanted to press only one key as a shorcut, it was ignored if
not preceded by any keystroke less than 0.5s before.

Changing order of time check condition solved it