Added a $stateNotFound event which can prevent or redirect state transitions.
Added lazy-state definition test.
Allow $stateNotFound handler to return a promise-like event.retry to defer state lookup retry.
Update README.md
Rewrote readme for improve consistency and cohesion

- Added top-level navigation
- Added 'report an issue' section
- Updated code examples to use latest APIs
Moving resources section below all code sections.
Added docs section link to top nav, contribute section
- Fixed misc. typos & formatting issues
Merge pull request #419 from angular-ui/readme

README rewrite
Small example code correction, fixes #424
Merge pull request #414 from Demeterr/add-stateNotFound

Added a $stateNotFound event which can prevent or redirect state transitions.