Add support for Material Design Icons

[huy-vuong]

Material Design Icons is a superset of Google's Material Icons iconset, adding community contributions that cover more use cases (glass of beer, croissants, etc.) than the Google's official version. They're especially useful for marking places, since it gives more specific options than a lot of other iconsets out there.

It'd be really useful to have them available so that, for example, having a marker with an icon named food-croissant would give back the food-croissant icon from that set. (To differentiate between Font Awesome and this, maybe mdi-food-croissant?)

[esm7]

Looks great, will add them.

[esm7]

Seems like this isn't a low-hanging fruit without support in Leaflet.ExtraMarkers, and when I went there to open a request I noticed that you already did :)