Custom params

@jrolfs 

When a collection is fetched, you can now pass in an additional ```params``` object of custom parameters.
I'm a little confused as to why we're so concerned about omitting the aforementioned keys from `filters` (and now `params`). Those options (`include`, `only`, `order`, etc.) should only ever be on the top level options object and not nested within `filters`. @cantino is there something on the backend that would break if a request accidentally included any of those special options nested in the filters param?