Update dependencies

Support Rails 4 and add rake to development dependencies.
Specify default task in Rakefile
Update appraisals

Add appraisal for Rails 4
Avoid specifying subject
Update factories DSL
Remove `spec/support/database.rb`
Outline updated API in README
Add pry as development dependency
Run specs in random order
Rewrite to match specification in README
Handle i18n deprecation warning
Add .travis.yml

Update gemspec for jruby