There has been a new major version, so it seems good to upgrade.

I had to drop two plugins:
- `asciidoctor-latex` seems dead, and hasn't had any commits since 2015.
- `asciidoctor-bespoke` also hasn't been updated for over a year, and
doesn't seem to be compatible with the new version.

During the last melpa-stable-packages update, there was an update script
invocation error which resulted in melpa-stable-packages to also include
all the unstable packages.

I have re-run the script correctly, so this commit removes all the
unstable packages that were accidentally included.

A commit in 2014 (see #2266) disabled building parts which depended on
X11 on Mac OS.  There's no explanation given in the pull request.  In
any case, many people install plan9port on Darwin specifically to use
the UI components.

Aside from this, the derivation was broken on Mac OS, probably because
people put the `which` and `perl` dependencies inside the !isDarwin
conditional.  Some programs worked, however the static libraries did
not build, so this could not be used as a buildInput to build programs
which need the libraries.  This fixes that.

trash: 0.9.1 -> 0.9.2

plan9port: build everything on Darwin

shelldap: init at 1.4.0

asciidoctor: 1.5.7.1 -> 2.0.10

melpa-stable-packages: remove unstable packages