Bump bash version (currently 4.3)

[Jeansen]

On project setup Bash v4 was current. Now, we are at v5.

• Update script to Bash 5 (there should bee some goodies available)
• Update version requirement

[Jeansen]

The new wait shoud be useful, as it waits for the whole process to finish instead of only a result change.

[Jeansen]

Not strictly Bash 5, but also very useful: coproc

[Jeansen]

Also of interest: SIGCHLD

[Jeansen]

And I should think about noclobber to make the script even more rigid!

[Jeansen]

Timestamps in the log could avoid calls to date, e.g. printf '\n%(%a, %d %b %Y %T)T\n'

[Jeansen]

printf -v could also be of some help.