Add support for USE_DOSEMU and BUILD_JSDOCS
from everything that links with the sbbs library. Also, use the absolute path to the 3rdp stuff to silence CMake warnings.
sbbs3 into the top-level list to avoid infinite recursion when a sub-projects include the sbbs3 list for libsbbs.so.
switchover to CMake.
DLL linkage to sort out though.
only so far. Next is making it work in Windows, then generic working on all other *nix platforms.