[wip] Introduce Wintermute::Util::Invokable.

  Wrote out base class for Invokable utility class. This allows classes
  in Wintermute to share a foundation of invocation logic without
  having to rely too much on machine implementation.
[wip] Improve Wintermute::Module.

  Reintroduced the Call header, thus fleshing out the structure of what
  Module::Call would look like.
[wip] Expand docs in Wintermute::Util::Serializable.

  Expanded documentation in Wintermute::Util::Serializable so that it
  became more clear how it was meant to be used. It exposed a few
  fallacies with the interface and some places we can improve it.
[wip] Nuke obselete code from Wintermute::Call.

  Removed a block of documentation that wasn't relevant to
  Wintermute::Call anymore and pulled out declarations of functions
  that weren't meant to be defined in Wintermute::Call.
[wip] Add two new source files.

  Add source code for Wintermute::Util::Serializable.
  Add source code for Wintermute::Util::Invokable.
Add docs and expand logic in macros.