add basic line numbering
Added support for files using the FileReader API https://developer.mozilla.org/en-US/docs/Web/API/FileReader

Tested on Chrome 28+ and Firefox 23.0
Updated README
Updated README with supported browser versions
Merge remote-tracking branch 'jigarvyas/master'
Merge remote-tracking branch 'ccin2p3/master'

Conflicts:
	css/zerobin.css
	js/zerobin.js