5.0.0-alpha1

• Now requires PHP 7.0.
• Depends on sabre/event 5 and sabre/uri 2.
• hhvm is no longer supported starting this release.
• #65: It's now possible to supply request/response bodies using a callback
  functions. This allows very high-speed/low-memory responses to be created.
  (@petrkotek).
• Strict typing is used every where this is applicable.
• Removed URLUtil class. It was deprecated a long time ago, and most of
  its functions moved to the sabre/uri package.
• Removed Util class. Most of its functions moved to the functions.php
  file.
• #68: The $method and $uri arguments when constructing a Request object
  are now required.
• When Sapi::getRequest() is called, we default to setting the HTTP Method
  to CLI.
• The HTTP response is now initialized with HTTP code 500 instead of null,
  so if it's not changed, it will be emitted as 500.
• #69: Sending charset="UTF-8" on Basic authentication challenges per
  [rfc7617][rfc7617].
• #84: Added support for SERVER_PROTOCOL HTTP/2.0 (@jens1o)