#182 pkgconfig file missing version

[Elliott Sales de Andrade]

The pkgconfig file contains Version: @VERSION@, but @VERSION@ does not seem to be set to anything in the CMakeLists.txt. So it just ends up being empty.

[Elliott Sales de Andrade]

Here's a super-simple patch that does that, but it does mean you need to update the version in two places. This could be avoided by running substition on clipper.hpp too if that seems annoying.