Provide an option to skip mandatory token

[ThomasG77]

I've made a Node/Express based server (mentioned in #16 (comment)) to replace the current Mapbox Markers API.

If I want to consume the server with your plugin, I need to fork it due to the mandatory token https://github.com/jseppi/Leaflet.MakiMarkers/blob/master/Leaflet.MakiMarkers.js#L60

Can you provide in the option a way to avoid it. A parameter like skipAccessToken with default value to false could do the job. I can make a PR if you agree on the principle & the approach.

[jseppi]

Sure, please do submit a PR!