Make the bash scripts path-agnostic

[lhchavez]

This change updates the bash scripts so that they can be invoked from an
arbitrary path. It also tries to be consistent of using braced, quoted
variables.

This is needed to fix htacg/tidy-html5#545

[balthisar]

@lhchavez, I had to undo this merge. When testing on a non-GNU versions of readlink, there's no -e option, and so the tools fail. I'll try to go back and cherry pick the other changes, e.g., the consistency with the quotes.

I'll miss the path independency, though. If you implement something without readlink, I'll be happy to merge that back in, too.

[lhchavez]

is this something reproducible on osx? i can try to get my hands on one and give it a try.

[balthisar]

Yes, and BSD.

[lhchavez]

thanks, and sorry about the breakage.

[balthisar]

No big deal. Usually macOS is the first platform I test on, so my bad for accepting it in Ubuntu only.