Add Guitar tab

[aminya]

http://usermanuals.musicxml.com/MusicXML/MusicXML.htm#TutMusicXML7-1.htm%3FTocPath%3DMusicXML%25203.0%2520Tutorial%7C_____8

https://usermanuals.musicxml.com/MusicXML/Content/EL-MusicXML-technical.htm