To make it easier to update individual modules, separate the call to
update() and the call to actually drawing the status.
Additionally, this avoids the "side effect" of updating when drawing the
status line.
Add a (half-finished) input library, that for now simply allows
registration and triggering of events.
As next steps, the trigger will happen as part of a separate thread that
reads input events.
Additionally, invoking commands via a execute() will be supported.
Thirdly, there is need of a way to selectively update the affected
modules (widgets), which should be possible given that the event
contains both the instance (widget ID) and name (module name).
Parse '-p' parameters and make them accessible via 'parameter()' from
within a module (basically, restore the previous configuration
facility).
Still TODO: Add support for configuration files.
The core.output module now manages the list of modules and retrieves the
widgets inside draw() itself. That way, details of drawing/updating
widgets are not visible from the outside anymore.
Add generic "draw()" method that redirects internally to the actual
calls. These can now produce JSON, which is nicer because:
1. Easier to use during testing
2. More flexible
3. Centralizes printing (somewhat)
Still, the "suffix" concept isn't really nice, but so far, I have no
better approach.
To maintain backwards compatibility (and because I think it's an OK
design choice), keep the widget concept (a single module can produce
multiple widgets).
