Some more cleanup.

- Removed VT100 font belonging to NETBOOT65.
- Removed machine / cart specific tests.
- Have Makefiles ignore errors on the clean goal.
General source code cleanup.

- Tab chars were partially used with the unusual width of two blanks. I removed them altogether.
- Line endings were inconsistent even iniside individual files. I normalized them.
- I introduced a consistent coding style regarding comment indenting and blank line usage.
- I removed trailing spaces.
- I removed newlines following unnamed labels.
- ...