Stringify IndexDefinition column names

* Other adapters construct IndexDefinitions from fetched strings
Fix unquoted string in README example
add MIT license metadata to gemspec
use HTTPS for URL in gemspec
Merge remote-tracking branch 'ktdreyer/gemspec-url'
Merge remote-tracking branch 'amarshall/patch-3'
Merge remote-tracking branch 'ktdreyer/gemspec-license'
Merge remote-tracking branch 'teleological/stringify-index-columns'