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.
Carl Lerche
Eliza Weisman