Post parameters in body, Accept header according to format, and new DSL options

* A new strategy for searching request endpoints.
* Support for `on: :collection` in addition to `on: :member`.
* Support for `except: [ ... ]` in addition to `only: [ ... ]`.
* Setting the Accept header according to the data format.
* Sending the parameter of a POST/PUT/PATCH/DELETE request in its body.