refactor controller update methods

pulled up the respond_to stuff into ApplicationController
respond_to_update
respond_to_create
respond_to_destroy
need to be refactored together.
add Renée's specs to README

I got tired of having to look at our issues to remind myself of the
spec.
Merge branch 'master' of github.com:Rails-Summer-Project-Noah-and-Matt/Library-Application
add libpg-dev dependency to README, closing (#73)
Merge pull request #71 from nbirnel/smell2

refactor controller update methods
fixed README.md