Add support for querying the version info at runtime.

[FreddieWitherden]

This is useful for applications which link against METIS as a shared library without access to the header file. At the moment they are in the dark about what options are available and what the data type sizes are. This PR adds a simple function to enable them to reliably query these facts.

[LecrisUT]

It would also be useful to expose these as compile-time constants. C++ would be easy to add that, do you thibk it can be added for plain C also?

[FreddieWitherden]

It would also be useful to expose these as compile-time constants. C++ would be easy to add that, do you thibk it can be added for plain C also?

This information is already available at compile time through defines, and so no changes are needed there.