Doc: Removed [fragment] from @lilypond examples NR (issue2810041)

[percival . music . ca]

Reviewers: ,

Message:
Docs look ok, but I'm not 100% certain about the changes to chords, or
whether Trevor wants us changing vocal.itely.

(this is a git-cl-merge of James Lowe's initial doc patch, and a few
fixes I applied to that one; I don't think it's worth separating this
into two separate patch-sets, but if you want, I could do that)

Description:
Doc: fixes for previous patch.


Doc: Removed [fragment] from @lilypond examples NR

Where appropriate replaced with [relative] or added { } construct within
@lilypond example

All except ancient.itely have been amended because some ancient music
examples gave unexpected results.

Please review this at http://codereview.appspot.com/2810041/

Affected files:
  M Documentation/notation/changing-defaults.itely
  M Documentation/notation/cheatsheet.itely
  M Documentation/notation/chords.itely
  M Documentation/notation/fretted-strings.itely
  M Documentation/notation/input.itely
  M Documentation/notation/percussion.itely
  M Documentation/notation/pitches.itely
  M Documentation/notation/spacing.itely
  M Documentation/notation/vocal.itely