Update L.TileLayer.MaskCanvas.js

remove ref to _protoCanvas
let data be an empty array
don't call draw if no _map property (i.e layer has been removed)
Update L.TileLayer.MaskCanvas.js

Put in version compare function that triggers a swap in of the old _createTile function if leaflet version is less than 0.7

Also made it so the setData function can take in an array of LatLng objects (tests first entry in array for instanceof LatLng)
Merge pull request #11 from martingraham/master

conditional use of _createTile