plexil-test

Pull request #41: Bring CMake to top-level directory

Merge in PLEXIL/plexil from feature/PLEXIL-102 to main

* commit '6a683c3ced0494de7064662efb69b8da70f4013c':
  Clarified cmake vs GNU make builds a bit
  Modified ReadMe as the source dir is now PLEXIL_HOME
  Bring CMake to top-level directory