Master

[NickFitz]

This moves the API keys (currently Google and Mapbox) to an external JS file, and demonstrates their use in an example file.

The 'm4h' object is created to hold the 'keys' object (rather than simply creating a 'keys' object as a global) as it might prove useful as a global namespace for holding any other properties, functions, or collections that prove to be needed.

No need to merge this if you'd prefer to approach this another way :-)

[AmeliaBR]

Ok, this is pretty much what I was doing, so I'll merge yours to master & then update my local WIP to use the same file & object names, so that I'll be able to rebase on this later without too much mess.