v0.13.0 - Application as a Function

This version introduces a major breaking change in the API. It implements a more functional
programming style.

Added

• Simplified request URI handling with a new Uri class to manipulate and deconstruct URIs.
  It is immutable and replaces individual URI components in Request. (#67)

Changed

• Application are now simple functions of Request -> Response. Middlewares become simple functions of
  Application -> Application. (#64)
• Request uri is now the full URI, reconstructed from server host and port. (#67)
• HttpStatus is now a class rather than an enum, which means custom HTTP statuses are supported. (#66)