Rename Router#pattern => Router#path
Update docs
Doc tweak
Use router path as key instead of full URL
Add router.currentHandlerInstance
Pass ref to current handler instance to willTransitionAway
Use "from" instead of "away"
Remove unused prop
transition example
Simplify promise-handling code
Re-throw errors from transition hooks

Fixes #21
Update app.js
Throw when a router cannot match the URL

This may not be a complete solution to #20, but it's better than
just showing nothing on the page and no error in the console to
indicate why.
Remove reduceRight, no longer applicable
transitionTo breaks the promise chain

Since we're effectively breaking the promise chain in the rejection
handler, we should just break the promise chain cleanly.
Fix broken specs
Use React-style singleton and names
Add URLStore spec
Use React-style singleton and module name
Ensure routers are only rendered once