adds format test for file stream
use `format_str` for a variable name since `format` is already method name
Merge branch 'master' into custom_format
Log format & column color are now customizable.

See `test_logging.py`:`test_custom_format()` & `test_logging.py`:`test_custom_color()` for usage.
removes `who_padding` feature since it is not consistent with `logging` module
sets reasonable default color
adds some docstring
Merge branch 'custom_format'