Added the BESM-6 simulator.

The SDL_ttf library matching the version of the SDL library must be installed and the font LucidaSansRegular must be present for the optional graphical panel feature.

A few standalone test scripts are present, as well as the OS boot script and the bootstrap code.
To run the OS, disk images should be taken from https://sourceforge.net/p/besm6/code/HEAD/tree/disks/

Some examples are in https://sourceforge.net/p/besm6/code/HEAD/tree/examples