add link to CAP theorem
(cherry picked from commit c52d7eb425b8649bd78dabbd180d9c220a7a6204)
link to complete
(cherry picked from commit b2e2d1f7b80708009a52a48bbb4c9e511a99095c)
remove Foursquare IDs
fix string/key consistency
Merge branch 'complete' into boilerplate

Conflicts:
	mongo_wrapper.rb
	test/mongo_test.rb
	test/mongoid_test.rb