Implement source in terms of stream

see https://github.com/scotty-web/scotty/issues/97
@alexbiehl You can use Haddock syntax in the deprecation message.  So if you put `stream` in backticks, it will get hyperlinked in the Haddock documentation.

In addition, you don not state that it is deprecated in the Haddock comment, recent version of Haddock take care of that.