BREAKING CHANGE: `RequestHandler` => `RequestMiddleware`. Middleware now
is expressed in terms of node core http.* types, which express req/res
are compatible with. Orienting to base http.* types allows better typing
accross all node servers, as eventually each implementation has these
values in their servers. That is to say, express, koa, fastify, next,
etc all use http.IncomingMessage/http.ServerResponse under the hood,
thus the new middleware types are compatible with everyone.

BREAKING CHANGE: `RequestHandler` => `RequestMiddleware`. Middleware now
is expressed in terms of node core http.* types, which express req/res
are compatible with. Orienting to base http.* types allows better typing
accross all node servers, as eventually each implementation has these
values in their servers. That is to say, express, koa, fastify, next,
etc all use http.IncomingMessage/http.ServerResponse under the hood,
thus the new middleware types are compatible with everyone.

…eware into refactor/types

…chimurai#722)

refactor: decouple from express