Review installation procedures in various scripts

[datasignals]

We should refrain of cd/pushd all over the place.
In most cases we are doing that just before performing a tar, git or zip but all these applications allow passing option -C for convenience.

See PR #34

[frgomes]

Being implemented as part of #57 branch:
https://github.com/frgomes/bash-scripts/tree/feature/0057-overhaul_turn_functions_onto_shell_scripts