release 0.10.0

0.10.0 (2014-03-02):
* Interface change: The `Request` and `Response` module types now explictly
  signal `Eof` and `Invalid` (for errors), to help the backend distinguish them.
* Interface change: Unify HTTP body handling across backends into a `Cohttp.Body`
  module.  This is extended by Async/Lwt implementations with their specific
  ways of handling bodies (Pipes for Async, or Lwt_stream for Lwt).
* [lwt] Interface change: HTTP client calls now raise Lwt exceptions rather
  than return an option type.  This permits better error handling in Lwt.
* [lwt] Interface change: The `Server` callback now always provides a `body`
  argument, since `Cohttp_lwt_body` now explicitly supports empty bodys.
* Add `Cohttp.Header.is_keep_alive` to test if a connection should be reused.
* [lwt] Respect the `keep-alive` header in the server request handling.
* [async] Add a `Body` that takes a `Pipe` or a `string`, similarly to Lwt.
* Install `cohttp-server` binary even if tests are disabled.
* Begin an `examples` directory with some simple uses of the library.