Better shellcheck support

[kins-dev]

Supports --enable=all for shellcheck https://github.com/koalaman/shellcheck/blob/master/shellcheck.1.md#options Adds shellcheck directives to properly source files

The major change was cleaning up every variable instance to be compliant with https://github.com/koalaman/shellcheck/wiki/SC2250

Thank you for having a good test suite. It caught a lot of the corner cases I missed initially.

Basically the main problem I was having is I run at a stricter level of linting than this project. So I brought it in line with the stricter set of rules. It shouldn't have any affect on people using a looser rule set.

[kins-dev]

Cleaned up most of the comments, also fixed a warning during make install: argbash.rst:42: (ERROR/3) Undefined substitution referenced: "OPTION_IN_PLACE".

Added to the make file missing examples

[matejak]

We are mostly good, I have left some remarks, then I will check out complex parts of the PR again, but I don't expect that much more issues will show up. Thank you once again for your effort, and patience that you have applied when designing this PR. The strict shellcheck support will be a great addition to existing feature set of Argbash.

[matejak]

Looks good, the only issue that remains is the generation of this example.

[kins-dev]

I apologize for taking so long to get back to this. I fixed up the patch file and generated the docs successfully. I think that's the last item.

[kins-dev]

Fixed up the docker workflow, I think that's everything