Version bump to 0.5.0.pre
Tests added to check that variables of type choices have specified a domain, closes #15.
Version bump to 0.5.0.beta
Fixed assertion
Version bump to 0.5.0.beta2
Tests added to make sure the JSON object `id` matches the variable file name, closes #17.
Version bump to 0.5.0.beta3
Use of Ruby 2.1.1 is now recommended
Version 0.5.0 finalized