Add subdomains option

While createTileLayer parses {s} correctly, you can't pass in the subdomains via TileJSON. While not in spec, this change allows that, due to the unique situation with leaflet-tilejson. Just add a new subdomains key, as an array or string, and it will pass through to Leaflet.
Update README.md

* Add subdomains
* Remove bounds, since they aren't used anyway
* Change from ${} to {s}, since it seems to be supported.
* Add subdomain note
* Since only the first URL is used, why show 3?
Add bounds support

It appears Leaflet always had bounds support on TileLayer, but [it wasn't documented until recently](https://github.com/Leaflet/Leaflet/commit/f2ab783dbf765f91fd865ea0b4f7d103974f8368). I just noticed it and decided to quickly add support, based on [MapBox.js](https://github.com/mapbox/mapbox.js/blob/mb-pages/src/util.js#L32)
Remove the bounds limitation from README
Merge branch 'patch-2'

Conflicts:
	README.md
Add bower
Bump package.json version, add robbiet480