Collapse job search

this adds the ability to handle collapsed job searches to the ruby api gem.  If collapse is off it will handle everything as it used to. But if collapse is on, it will go down the collapsed path and return a Cb::Models::CollapsedJobResults insted of a Cb::Models::JobResults
A more positive-leaning boolean expression for this - just looking for the key in the hash body:
```ruby
response[root_node].key?('GroupedJobSearchResults')
```