Refactor #new, ::create, ::create! to require explicit Array argument.

Current spec status:
  standalone: 76 examples, 0 failures in 0.11159 seconds.
  ActiveRecord 4: 140 examples, 0 failures in 0.18072 seconds.
Implement #update_attributes with array of params hashes.

Current spec status:
  standalone: 87 examples, 0 failures
  ActiveRecord 4: 162 examples, 0 failures
Add #update as alias for #update_attributes.

Current spec status:
  standalone: 89 examples, 0 failures.
  ActiveRecord 4: 166 examples, 0 failures.