add acts-as-taggable-on

gem 'acts-as-taggable-on'
bundle install
make books taggable

rake acts_as_taggable_on_engine:install:migrations
rake db:migrate
Book acts_as_taggable # Alias for acts_as_taggable_on :tags
BookController params.permit :tag_list
add tags to books show
Merge branch 'master' into tags

Conflicts:
	Gemfile
	Gemfile.lock
	app/controllers/books_controller.rb
	app/models/book.rb
	app/views/books/show.html.haml
	db/schema.rb
add tags in index, show, and form

TODO: make tags in show clickable links
Merge pull request #79 from nbirnel/tags

Tags