Moved WordId into the Language.Forth.Word module.
Removed unused Language.Forth.Interpreter.Input module.
Cleaned out some old dead code.
Execution token (XT) is now really the the execution semantics.

Previously it embedded a Forth word, but having the execution
semantics is more in line with how the standard specifies it.
Added - and 0=

Introduced binary arithmetic helper function to implement + and -.
0= allows for zero values and null address pointers.
Corrected branch and branch0 to use 'ipdo'.
Refactored compile to work on any reasonable cell value.
Added COMPILE, to Primitive and the dictionary.
Refactored INTERPRET to be implemented with a docol Forth word.
Minor move of searchDict function.
Renamed xword to word.