Rewrite focusing to use textarea (still a few display issues to sort out)

See #3, #4
Miscellaneous fixes

* Remove focus outline from textarea (see #4)
* Fix textarea clearing with timeout of 0 (not perfect, but works for most cases)
* Math.randInt
* Test/demo tweaks
Miscellaneous fixes

* Remove focus outline from textarea (see #4)
* Fix textarea clearing with timeout of 0 (not perfect, but works for most cases)
* Math.randInt
* Test/demo tweaks
Merge branch 'focus' of https://github.com/lethosor/js-df-tileset into focus
Merge branch 'master' into focus
Remove extra whitespace