Video now working!

Re-wrote the guts of PiCamera: split out all the encoder creation and
configuration logic into some separate private classes customized for
still and video capture. Discovered resolutions can't be set separately
(setting one sets them all) and video capture only works when all
resolutions are synchronized so there's now just one "resolution"
property. Tested video capture and it seems to work well (better at
lower resolutions).
Merge branch 'master' of github.com:waveform80/picamera

Merging release 0.1 tag