Support adding to map after map init

This change supports adding the control to a map via "map.addControl(
L.Control.loading() );" as an alternative method along side the already
supported map options method.
(Includes the concept of hashed loading states.)
Merge remote-tracking branch 'origin/master' into postdefacto-addable
Tabs -> spaces
More compatible check for members of _dataLoaders

Previous method was not IE 7/8 compatible.
Remove redundant comments
Contributing
gitignore
Contributors as a list
Use the MIT License
Move map attachment

In the context of ex post facto control addition, it makes much more
sense to attach the control to the map in the onAdd function.
Merge branch 'expostfacto-addable' of git://github.com/codefox421/Leaflet.loading into codefox421-expostfacto-addable
Consolidate layer event logic
Leaflet 0.6