Remove observers et. al

[desmondmonster]

Here's progress so far:

• removed observer support & tests
• ActiveSupport Logger default format changed; made tests care more about relevant details
• mimicked mass assignment sanitizing that was relied on to remove an :index key before model attributes were set

TODO:

• create a compatibility module to adapt mass-assignment method calls
• Dirty tests are still failing. If you inspect the post.changes hash on spec/examples/dirty_spec.rb:227, instead of having the two comments it has two nils. I haven't figured out yet why this is so. Open to suggestions, but meanwhile will keep digging.