Trying to add a debugger again.

Probably should start a development branch.
Added warning switch to dmd build command.

DMD does not show warnings by default.  Finally woke up to that fact.
Also removed an extraneous file (src/debugger.d)
Attempt to make elements conform to a standard.

Added Configure and SetPagePosition as interface methods that must be
implemented.  Which also means all elements must connect to dui and
reconfig events.  (dui ... silly name)