Add suggest completion support to tire

As per http://www.elasticsearch.org/guide/reference/api/search/completion-suggest/

I am aware there is another pull request on this subject: https://github.com/karmi/tire/pull/777 but it only implements the term and phrase suggest apis and not completion api wich me and my team needed at the time.

I'd like to hear @karmi and everyone else's opinion on how to proceed with merging the work me and @marc-villanueva did before advancing further.

I know some of the pending tasks for this branch to be in a mergeable state are:
- use ruby 1.8 hashes 
- Fix tests for elasticsearch v0.90.1 
- Write integration tests