High priority:
* option to cover up error messages with blank image
* option to limit image width (not sure if height will be restricted)
* either replace post content after tag change, or just eliminate
  tag setting and hardcode to some value
* limit number of fragment in comment
* limit length of content per fragment

Others:
* implement MusiXTeX support
* implement MusicXML support (this one can be difficult)
* implement PMW support
* implement lilypond-book syntax support
* chroot support for lilypond