+ typedef, __func__, bugfixes, improvements

Add support for:
- typedef
- __func__ (predefined identifier (array of char) containing the current
function name)

Bugfixes:
- improve parsing and error checking of void and incomplete declarations
- properly truncate offsets of local vars in generated 16-bit code

Improvements:
- main() returning without 'return' now returns 0
- checking for invalid/unknown command line options

Misc:
- test updates