Fixed security issue with gemspec file.
Updated to 0.6.2.
* depends NotNaughty 0.6.2
* added content to README.rdoc
* updated docs of uniqueness validation, parts taken from ruby sequel
* require correct version of not-naughty
* don't add a release when run release task, just add the file
* split from not-naughty gem
* added gemspecs for github
* added uniqueness validation with scope [resolves:#19650]