fork.js instance methods refactoring:
  - set_source( source ): disconnects fork from previous source if any, then connect to source if defined.
    This new method to manage connections is designed to be the basis of all other connections methods while
    improving the semantics and removing any ambiguity over the name of the former connect() method.

  - refactor disconnect(), to(), not_from() to all use set_source()

  - connect() is now a deprecated alias of to(), will be removed soon

  - from()    is now an alias of set_source()
  - not_to()  is now an alias of disconnect()