php://input specific stream implementation

- Prior to 5.6.0, php://input is read-once. As such, this implementation adds
  caching of the stream so that it may be retrieved multiple times.
Use PhpInputStream by default in Request

- If $stream passed is 'php://input', creates a PhpInputStream
  instance.
CS fixes

- unused use
Updated changelog
Merge branch 'feature/php-input-request'

Close #3