added support for clefs

* soprano
* mezzo-soprano
* baritone-c
* baritone-f
* subbass
* french

also updated celf_test.js

in particular refacored clef change test to show c4 for every clef
change, easing evaluation of correct note placement
removed trailing comma

otherwise would brake IE
updated clef.js commenting style

to match new commenting guidelines of vexflow
Fix comments and lint errors.