MacOS files

created some MacOS specific files. bundle.sh wraps the executable in an
OS x Application bundle, and info.plist is a property sheet needed by
that bundle.
Makefile
Modified Configuration to work on OS x platforms.
Resolved some compiler warnings

chesspp::exception::what was hiding std::exception::what.

Fixed initialization list order in Piece ctor, and gave Piece a virtual
destructor because it's an abstract class.