Require ruby 2.0.0, activerecord 4.1

* arel dependency is unnecessary
Update Gemfile, drop jruby support

* Use https rubygems url
* Update appraisal version
* Remove activerecord dependency - it is defined in the gemspec
Update appraisals. Test against ActiveRecord 4.1+
Stop the Rakefile insanity

* Use standard bundler gem tasks
* Use standard rake test tasks
Use mintiest

* Drop support for old Arel versions
Update gemspec, remove ".nonrelease" from version

* Add minitest development dependency
Version 0.6.0

* Remove versionomy cruft
* Remove Version file