This changes the Service request type to a generic instead of an associated
type. This is more appropriate as requests are inputs to the service.
This change enables a single implementation of `Service` to accept many
kinds of request types. This also enables requests to be references.
Fixes#99
A dual MIT / Apache 2.0 license does not make any sense. Since the
intent of the original license was to be dual under MIT or Apache 2.0,
restricting to ony MIT is OK.
