Whenever a new bar is being drawn, log out all parameters that were not
used at all. This might indicate a bug in the module, or might point to
a spelling error in the parameter name.
fixes#494
Add an interface that allows arbitrary objects to store/retrieve
arbitrary key/value pairs. This will be used for different purposes in
the future:
* Config class(es) can store user-defined parameters for modules
* Widgets can store state
* ???
see #23