Fixes
- check if movie/track really exists each time we call it
- add rdocs
- fill README

Features
- export a single frame as pict
- resize movie
- export image sequence
- import image sequence
- import other file formats (mpeg, aiff, mp3, etc.)
- get movie metadata (album, author, artist, etc.)
- set movie metadata
- programatically adjust export settings (framerate, codec, etc.)

Possible
- add text track to movie
- add chapters to movie
- time remapping