Updates to use flacthis as module import

Improved support for using flacthis as an import module, cleaned up some inconsistent formatting issues with PEP8, added additional comments to the readme for module support, and included some basic testing for encoder/decoder and directory issues.

Also updated some of code handling encoder/decoder checking (I was having issues on my system where ffmpeg's not compiled with some of the encoders).  

This is a handy script - I use it as the back end for some of my personal scripts handling my media library.