first step towards V3

I started using tagsmanager in a new project and I wanted to play with typeahead.js, so I added a new initialization parameter called "version_three" which is by default set to "true" (maybe that's a little bit too optimistic). It disable bootstrap typeahead.
I am using it with typeahead.js and integration seems simple (done outside of tagsmanger using typeahead.js api and tagsmanager api), I will post a sample by the end of the week I promise.

I also fixed a bug in pushAllTags, and added a new method "tags" which simply return a json containing all tags
entered.

@johnnyshields  I am pushing this as a pull request to collect comments from everybody.