This is an example page for Leaflet.ShowAll
Check out the source code, it's super simple!
Leaflet.ShowAll allows you to zoom out to show the entire area, then zoom back in to the same view you were just at. You can move around
while in show-all mode, but if you zoom in or out you're out of show-all and your previous view is lost. Here you can also double-click
on the marker to go back to the original view.