The C++ Reactor class doesn't own a reference to the Func object. To make
borrowing the reference safe, the Python Reactor class now owns a reference,
which is guaranteed to be valid for the lifetime of the C++ Reactor object.
These changes make it unnecessary to copy header files around during
the build process, which tends to confuse IDEs and debuggers. The
headers which comprise Cantera's external C++ interface are now in
the 'include' directory.
All of the samples and demos are now in the 'samples' subdirectory.
