Adding total runtime print message

[ZachJHansen]

Closes #64

[teiesti]

I am against this change, at least in its current form. My reasons are:

1. You can always time a command on the runtime with time <command>, giving you not only the walltime but also the respective CPU times.
2. When translating, the output is currently your expected program or theory without any additional elements. Adding the time at the end makes it much more difficult to chain various translations, e.g., anthem translate --with tau_star foo.lp | anthem translate --with gamma. Of course, we can circumnavigate this concern by printing additional information to stderr.