Dropped support for rails 2.x. Added support for Rails 4.

Updated to rspec 2.14.0. Updated specs to work with Rails 4. Added
Rails 4 to Travis config. Bumped version to 2.1.0

Need to update readme.
Need to changelog with any other commits that were added since 2.0.0
Remove hanna as a development dependency.

It's long-unmaintained.
Rely on RDoc::Task rather than the defunct Rake::RDocTask