merges manubot/rootstock#483
merges manubot/rootstock#486

Co-authored-by: Laurent Perrinet <laurent.perrinet@univ-amu.fr>

merges manubot/rootstock#484

refs manubot/rootstock#485 (comment)

Some users might have their repository workflow permissions
set to read only. This change should ensure the workflow job
can write commits back to the output and gh-pages branches
on GitHub.

merges manubot/rootstock#487

* add width/height to mastodon icon in front-matter
* update mastodon icon from Front Awesome
* remove dimensions from SVG files, since these are specified in
   the front matter.

Co-authored-by: Vincent Rubinetti <vince.rubinetti@gmail.com>

merges manubot/rootstock#489
closes manubot/rootstock#488

* environment: add librsvg
* add note about using SVG files from URL and exporting to docx

merges manubot/rootstock#493
closes manubot/rootstock#492

* Set write permissions in AI workflow
* Add pull-requests write permissions

merges manubot/rootstock#498

merges manubot/rootstock#501

CI: install environment using mamba.
mamba is faster and has better error messages than conda.

build/README.md: add mamba instructions to create environment.

merges manubot/rootstock#503
closes manubot/rootstock#500

required to address:
cannot import name 'RequestRate' from 'pyrate_limiter'

merges manubot/rootstock#496

refs manubot/rootstock#508
merges manubot/rootstock#509

Fixes appveyor install error:
> The repository 'http://apt.postgresql.org/pub/repos/apt bionic-pgdg Release' no longer has a Release file.