Modified sessions#create to check both email and username for login
Changed the sign_in form and the parameter being passed to username_or_email
Made tests work with new parameter name
Changed signup form and added notes for the future

Conflicts:

	app/views/users/new.html.erb
Changed login parameter to identifier and cleaned up sign_in view
Added scope for finding a user by their email or password and implemented it in the sign_in process

Conflicts:

	app/models/user.rb
Removed extraneous sign_in link on sign_up page
Changed sessions controller test to reflect parameter name change
Merge pull request #4 from 4bstractor/identifier_login

Identifier login