gplugin/gplugin

Prepare for the 0.31.0 release
v0.31.0
2021-05-27, Gary Kramlich
f25e021e4053
Prepare for the 0.31.0 release

Testing Done:
ran `ninja dist` as well as `ninja all doc test` on the resulting tarball.

Reviewed at https://reviews.imfreedom.org/r/676/
The following individuals have contributed to this project.
Ankit Vani <a@nevitus.org>
EionRobb <eion@robbmob.com>
Elliott Sales de Andrade <quantum.analyst@gmail.com>
Gary Kramlich <grim@reaperworld.com>
Jason Scherer <schereja@gmail.com>
John Bailey <rekkanoryo@rekkanoryo.org>
Mike Ruprecht <cmaiku@gmail.com>
Olaf Hering <olaf@aepfle.de>
Richard Laager <rlaager@pidgin.im>
Sorvival <sorvival@tutanota.com>