libresource: Docs - Fix documentation on two functions

mrp_res_list_attribute_names and mrp_res_get_attribute_by_name
had the wrong return type as well as an extraneous parameter.
libresource: Add context to resource sets, set a set for listing resources

This enables the removal of passing of contexts and resource sets
unneededly.
libresource: Remove context from mrp_res_set_autorelease()

Also add context to the privates of mrp_res_resource_set_t
libresource: Remove context from (mrp_res_)delete_resource_set
libresource: Remove context from mrp_res_copy_resource_set
libresource: Remove context from mrp_res_acquire_resource_set
libresource: Remove context from mrp_res_release_resource_set
libresource: Remove context from mrp_res_get_resource_set_id
libresource: Remove context from mrp_res_create_resource
libresource: Remove context from mrp_res_list_resource_names
libresource: Remove context from mrp_res_get_resource_by_name
libresource: Remove set from mrp_res_delete_resource
libresource: Remove context from mrp_res_list_attribute_names
libresource: Remove context from mrp_res_get_attribute_by_name
libresource: Remove context from mrp_res_set_attribute_string
libresource: Remove context from mrp_res_set_attribute_uint
libresource: Remove context from mrp_res_set_attribute_int
libresource: Remove context from mrp_res_set_attribute_double