Move config code from railtie to redis-kit proper.
Add tests for bad config files, improve error messages.
Add tests for the base gem methods.

Also, I've added a custom error class for invalid YAML syntax.
Update tests for JRuby.
Allow MockRedis as a configuration option.

This is useful for tests / development, as long as you don't
go beyond MockRedis's feature set.
Raise an error if the config file is blank.
Merge branch 'develop'