Add option to get the ChordPro {define ...} text from Chord Finder results

[jonthysell]

From the ChordPro format http://www.chordpro.org/chordpro/index.html:

{define ... }	Defines a guitar chord. There are several variant implementations of this command. Chordii: {define:name base-fret offset frets pos pos ... pos} pos … define the string positions, all relative to the offset. Strings are enumerated from left (lowest) to right (highest), as they appear in the chord diagrams.

This should be easy to do with the ChordFinderResult items, as I already have the base-fret offset and relative positions.

[jonthysell]

ChordPro 5 spec: https://github.com/sciurius/chordpro/wiki/Directives-define