Remove Appraisal, use WWTD
Consolidate gem requirements into gemspec
Be explicit about the activesupport dependency

lib/active_record_shards/configuration_parser.rb explicitly requires
active_support/core_ext
Remove run_tests script, use wwtd instead
Stop testing against Ruby Enterprise Edition
Merge pull request #27 from zendesk/bquorning/wwtd

Remove Appraisal, use WWTD