Version 2.5.1 - some fixes

This version fixes a bunch of errors, as reported by Keith Howell (thanks!)

• LABEL EQU 123 ;strips comments from listing fixed
• FCC "string" was not implemented. fixed
• DS "something" was silently done, totally disrupted the code. fixed
• EQU something without a label now throw an exception.
• M6800 assembler has a problem with an empty comment line. fixed