Modular api to satisfy #68

This implements a superset of the API mentioned in #68 with addActions/addStores supporting the current object format (and used by the Flux constructor), and addAction/addStore supporting the one-at-a-time notion.  

Flux#addStore takes a name and a store, and adds the store to Flux.

Flux#addAction takes either an array of namespaces and an action function, or any number of namespaces as strings, and then an action function.   

bindActions was changed to throw when encountering a collision.

I didn't check in any documentation, but I can do so if you'd prefer that to writing it yourself.