Add current coordinates to URL

[jahands]

This will allow people to link to specific parts of the map:
https://github.com/KoGor/leaflet-fullHash

Here's how I use it (I'm not sure how this translates to L.CRS.Simple maps): https://gist.github.com/jahands/04e145d0b0f7be66ff930fc48aaf82eb#file-leaflet-main-html