Clean up and improve nearly all the code.

The `links` and `assets` methods are a bit "too clever", but I still find them
quite readable and prefer their current implementation to previous ones.

Remaining TODO:
  * rspec or test::unit, including mocks
  * Simple server + Coffeescript + D3.js integration
Standardize on href for string, uri for object.
Fail gracefully
Fix www subdomain