Include git commit ID in version data and introduce 'version' command

[hogsy]

Some solutions are provided here though they're not great.

Should ensure that this is printed to the logs as well, as this will make tracking down some faults a little easier.

[solemnwarning]

Its not perfect, but I usually put -DVERSION=xxx in the CFLAGS as necessary (see here).

[hogsy]

Another solution is provided here though it will only work each time CMake is run.

http://xit0.org/2013/04/cmake-use-git-branch-and-commit-details-in-project/

This might not be too bad, because it still means our releases will have the correct information.