Rename files to lowercase
dis31: compiles under Linux with GCC

Cosmetic changes to port the source.
Made sure it still compiles with Borland C 3.1 for DOS (for fun)
entertab: compiles under Linux with GCC
src/D8031.PRJ: Borland C project for the interactive shell
The interactive shell d8031 builds under Linux with GCC
Interactive shell for 65c02 compilers for Linux with GCC

Unfortunately the messages are in Cyrillic with code table KOI-8.
Still, the disassembler works.