Add ArrayLike maker 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. For more info, see

https://github.com/dribnet/ArrayLike.js
Merge pull request #7 from dribnet/isArray

add ArrayLike.js marker for interop with other js libraries