Bump version to 0.2.0.dev.
Drop support for Rails 4.0.0 and support only 4.0.1 and above.

Rails 4.0.0 introduced a backwards incompatible change to order scopes
and 4.0.1 reverted the change. Given the short-lived nature of the BC
break, we will no longer support Rails 4.0.0.
Add license details to gemspec.