Cleaned up and extracted base functionality

Gianfranco,

Jesper and I cleaned up this script to work with:
- MacOS (e.g. mktemp /tmp/AWKPRACTICE_XXXXXXXX)
- run test from any directory
- run scenario_XX.bash from any directory
- use answer_XX.awk for each exercise

Feel free to import changes and see if it runs.
Alternatively, you could clone my repo and test if runs on your environment.

I will do test on cygwin later.

Cheers!
n.