Tags pagination refactored to only include public tags
Fixes 36

 * Refactor ActsAsTaggableOn::Tag.public_tags to find distinct public tags via a subselect instead of SELECT DISTINCT clause
   * The subselect is not only faster, but `size` works properly
   * `size` was stripping the SELECT DISTINCT clause when generating a SELECT COUNT(*) query
 * Remove default_scope since it was adding unnecessary ORDER BY clause where it was not needed
 * Move the default_scope to a normal scope called ordered_by_slug
   * Only use ordered_by_slug where it is needed such as MyGists::Search
Add missing TomDoc [ci skip]
Merge pull request #37 from simeonwillbanks/tags-pagination-bug

Tags pagination refactored to only include public tags