RF+DOC: note about needing to download flac

- also, maybe slightly safer not to hardcode a path to `which`
RF: add a pref to set path for flac executable

- also reorganize _getFlacPath(), log flac version
ENH: speech_recognition coder demo

- no longer get Error about named color space
RF: minor code format clean-up
Merge pull request #348 from jeremygray/master

flac path as a pref, better doc about downloading flac