Some minor bug fixes and improvements:

- Fixed a bug in FN key codes that lead to the activation of the wrong FN keys;
- introduced support for NMI custom routines (suggested by nippur72) with NMI statement;
- fixed a bug that lead to un-wanted behaviors when graphic chars were parsed in direct mode.

Grab the code from my Github repo: https://github.com/leomil72/LM80C