bibclean 2.16 (new formula)

* Build failed with superenv, hence included `env :std`.
* `ENV.deparallelize` was also necessary.
* Two `inreplace` statements insert `mkdir` statements needed on MacOS.
* One `inreplace` statement fixes the `mandir` variable in `Makefile`,
since it is not properly defined by autoconfig despite the `--mandir`
parameter passed to `./configure`.
Let's write a wrapper script to set the PATH to include this directory instead. Nicer to do these things automatically when we can.