Manually supply the AES encryption keys to ffmpeg

Update README

Always store latest used api url in json

Use OS-provided random port for dir server

Download only 1 audio stream

Handle lectures with only one angle

* Update build file

* Report ffmpeg errors to user

* Ensure proper cleanup of temp files

Default to http for course_url

Bump version

Bump version

Add support for bitshyd.impartus.com