editors/pluma: switch to GitHub source
Switch from MATE mirror to GitHub tarball using USE_GITHUB and
GH_ACCOUNT=mate-desktop, add autoreconf, mate-submodules GH_TUPLE,
autoconf-archive, yelp-tools, common:build, patch configure.ac and
docs/reference/Makefile.am to remove gtk-doc, and remove stale API
doc plist entries