observable 0.5

- Fixed a harmless warning about an uninitialized __observer_map variable
  when assigning to an observable var before setting up any when clauses.
  Thanks to Hadmut Danisch.
  
- If an observer proc takes 3 args, then the third arg is assigned the object
  being observed. If it takes 4 args, then the fourth is assigned the name of
  the attribute. This is useful if there are a lot of objects or attrs. See the
  examples/mem-usage-*.rb for examples and discussion. Thanks again to
  Hadmut.

observable 0.4

- Marshal and YAML compatibility: Objects with registered observers can
  be dumped, but the dumped versions lose their observers, of course.

- API change: Renamed stop_observing to remove_observer.

- API change: signals are now fired by methods of the form #name rather
  than #name=. There is no longer a reader method associated with
  the signal (the method that used to be called #name). Signals are
  intentionally valueless except at the instant of firing, and at that
  time the value is available as the argument to when_ clauses.

- Added tests.

observable 0.3

- Now supports distributed observers with DRb. See the chat-server.rb
  and chat-client.rb examples in the FoxTails package.

- handle_observer_exception: a mechanism for handling exceptions in
  observer call-backs.

- Having an observable attrs also gives you "stop_observing_#{var}".

- Signal handlers now complain about reentrant calls.

- Added tests.

observable 0.2

- Added signals. See the docs and examples.

observable 0.1

- First public release.
