Print tag/short commit hash to screen and logfile. Fixes #23

This adds a CFLAG to pass the latest tag followed by a short commit hash and print this out to the .klg file and screen.

This prints out the value of:
```git describe --abbrev=4 --dirty --always --tags```

An example might be: ```november_2014_single_processor-14-g9af1-dirty```

which means: ```14``` commits past ```november_2014_single_processor```, git commit beginning in ```9af1```, and the ```-dirty``` indicates that there are uncommitted changes.