Coordinates incorrect at or beyond -85, -180, 85, 180

[dankarran]

When moving the mouse above or below the latitude bounds (85º for Mercator maps), the latitude value should probably be capped at 85º.

When moving the mouse east or west beyond 180º, the longitude value should show the correct longitude for that copy of the world rather than continuing past 180º or -180º.

[dankarran]

I've added a fixLng method which seems to do the trick for longitude values: https://github.com/dankarran/Leaflet.MousePosition/commit/d006373b2053a47cf69e46d3b4acf432420ba4bd