[#916] Added support for the Suggest API (@marc-villanueva)

See: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-suggesters.html

Related: #916, #894, #857, #777
[#857] Added support for the Suggest API (@fbatista)

Still needs more tests and support for other more types other than completion

See: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-suggesters.html

Related: #916, #894, #857, #777
Added suggest support to the model integration

Related: #916, #857
Suggestions: Exception raised outside `Search` module, use fully-qualified name.
Suggestions: Shortcut method in DSL
Suggestions: Fixes for completion multi
Suggestions: Integrated @marc-villanueva stuff with @fbatista PR

Related: #777 and #857
Suggestions: Fixed failing unit tests
Suggestions: Working integration test within search
Suggestions: Integration test for standalone completion
Suggestions: Integration test for standalone suggestions
Suggestions: Allow options for completion
Fixed failing test on 0.90.7
Suggestions: Added information about the topic into `tire-dsl.rb` documentation
Suggestions: Small edits to the relevant chapter in `tire-dsl.rb` documentation

Closes #916
Closes #894
Closes #857
Closes #777