README.md: Include Mizar32-C as a supported platform
SConstruct: Remove MY-BASIC from the list of supported languages

Martin was right! MY-BASIC was a horrible idea. We'll surely have
Forth though (and probably Haskell, but the test results with Hugs
don't look very promising).
inc/shell.h: Remove MY-BASIC from the list of supported languages
src/main.c: Remove MY-BASIC from the list of supported languages
src/common.c: Remove MY-BASIC from the list of supported languages