manpage: add sections and order by usage

Split the options into the following sections:

 * Playback Control
 * Program Behaviour
 * Video
 * Audio
 * Subtitles
 * Window
 * Disc Devices
 * Equalizer
 * Demuxer
 * Input
 * OSD
 * Screenshot
 * Software Scaler
 * Terminal
 * TV
 * Cache
 * Network
 * DVB
 * PVR
 * Miscellaneous

Most options are sorted by usefullness and how often they're used or how
important they are.
This makes finding the right options easier and adds some sort of structure.