Add L.LocationShare - Client-Side location sharing

Add Leaflet.LocationShare, allowing users to send and receive markers via url. [Demo](http://cliffcloud.github.io/Leaflet.LocationShare/)

[Demo #2](http://cliffcloud.github.io/Leaflet.LocationShare/?lat=39.20671884491848&lng=-76.86035156249999&M=Here's%20where%20this%20plugin%20was%20written!) with received location