address issues #3 and #12

The single `gh` object has been added and all public classes/objects
attached to it, solving issue #12. I've also begun work on issue #3,
by renaming the TextBox class to TextSprite, but no other changes have
been made. As a result, that issue will remain open.
bug fix in Sound/web audio api
Merge pull request #19 from sedabull/api-changes

Api changes