Pre-include predefined guitar fretboards for lily role #28
Description
For example, if we want to show a fretboard diagram of D7 chord in the lily role, we need to write:
:lily:`\include "predefined-guitar-fretboards.ly" \new FretBoards{ \chordmode { d1:7 }}`
obviously, the following one is more convenient:
:lily:`\new FretBoards{ \chordmode { d1:7 }}`
