Closes #18

[rosnovsky]

A new slug option was added. It's backward and forward compatible.

{
  name: 'tags',
  title: 'Tags',
  type: 'tags',
  options: {
   ...
    // Turns tag values into lower case slugs. Labels remain unchanged. Defaults to false. 
    // Tags created after enabling this option will remain slugified after you disable it.
    slug: true,
  }
}