feat(shell-tools): Add check.sh scripts for a quick smoke test

[blorente]

Changelist

While reviewing PRs from students, I found it useful to have a small script that runs their solution along with the relevant unix utility, and compares the output. Here are those scripts.

Usage examples:

$ cd implement-shell-tools/wc
$  ./check.sh  #Will test "node wc.js"
$  USER_COMMAND="python3 wc.py" ./check.sh

[illicitonion]

Thanks!