Raise a rescuable exception when Rails doesn't know what to do with the format, rather than responding with a head :not_acceptable (406)

We should let the responder to decide what to do with the given
overridden response block, and not short circuit it.

Fixes #5280

Closes #5025 part 2

Default responder was only using the given respond block when user
requested for HTML format, or JSON/XML format with valid resource. This
fix the responder so that it will use the given block regardless of the
validity of the resource. Note that in this case you'll have to check
for object's validity by yourself in the controller.

Fixes #4796

There're a lot of places in Rails source code which make a lot of sense to switching to Object#in? or Object#either? instead of using [].include?.

So we don't miss out on the nice documentation of the respond_to and
respond_with instance methods.  Also added :nodoc: to protected method.

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Explain in the method doc that you need to call respond_to at the class level in order to use respond_with.

Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

Correctly handle the case of an API response that returns a hash by treating a single hash argument as the resource instead of as options.

Signed-off-by: NWincent Colaiuta <win@wincent.com>

Signed-off-by: NWincent Colaiuta <win@wincent.com>

Ensure details are frozen after @details_keys lookup. The implementation waits to freeze until the last required moment, to avoid duping hashes.

Improve performance of the rendering stack by freezing formats as a sign that they shouldn't be further modified.

Finish cleaning up rendering stack from views and move assigns evaluation to controller (so plugins and/or controllers can overwrite just one method).

Unify class_inheritable_accessor and extlib_inheritable_accessor and allow responder to be set in the class level.