use correct scrollWidth values

my.scrollWidth was never defined in timeline.

this.drawer.scrollWidth was removed in other commit
Add 'scroll' event
Dynamic scrollbar work

Use the current size of the scrollbar instead of the one set at initialization (user might have resized the window)
Dynamic scrollbar work
Add 'scroll' event documentation
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/drawer.js
	src/wavesurfer.js
Merge pull request #233 from rgagnon24/master

Add 'scroll' event, use Dynamic width of container