Add git hash to version number display

[prpr19xx]

It would be useful to add the the git hash to the output from jimsh --version
Rather than just outputting e.g. "0.82", it could output with some or all of the git describe output
e.g. "0.82-82-ge23aea2" or "0.82 e23aea2" or "0.82 0.82-82-ge23aea2"
or whatever format you think best.