Alternative chord sets for songs

[grotsztaksel]

When a song defines more than one set of chords separated by the chord separator (see the XSD):

<verse>
  \Blah \blah \blah     | e A B  |  g C D
  ...
</verse>

then

• this XML should result in two HTML files, each containing the song with either of the chord sets
• only one of the HTML files should be linked to in TOC
• each of the versions should link the others
  some ideas:
  • Below the title, above the first verse
  • on the chords (makes sense only for CHORDS_BESIDE mode)