A series of refactorings

* Renames PlaylistControls#process_raw_playlist to PlaylistControls#parse_playlist
* Extracted constant from raw playlist parse regexp
* Removes comment line from Gemfile
* Changes one liner methods to multi line
* Changes `if not running?` to `if stopped?`
* Changes trenary expression for conditional exit point at MediaControls#volume
* Extracts VLC::Server#process_spawn and VLC::Server#process_spawn_ruby_1_8 from VLC::Server#start