add ArrayLike.js marker for interop with other js libraries

Add a marker to make array compatible with other libraries
via either the ArrayLike polyfill or with libraries that
support the ArrayLike.js specification.

An example of this allowing interop with leaflet.js is here:

http://bl.ocks.org/dribnet/4326899

More information available here: 

https://github.com/dribnet/ArrayLike.js