Previously, you could not use `List<Vec<MyService>>` as a type, because
`List<T>` required `T: Iterator`. Instead, you'd have to write
`List<std::vec::IntoIter<MyService>>`, which gets really bad for
complex iterator types. This change instead makes `List<T>` require
`T: IntoIterator`, and then store `T::IntoIter`. This is a little weird
intuitively, but makes writing out the type for a `List` much more
pleasant.
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.