Update changelog with changes made by all PRs merged since the last
tagged version, except for those invisible to the end user (changes to
CI workflow, changes overwritten by newer PRs, etc.)
Fixed formatting in changelog to be more consistent
Fixed grammar and punctuation in changelog
Userguide v2 was never, the old one was deleted. It is still out of date and currently doesn't even build.
Signed-off-by: Stephan Lachnit <stephanlachnit@protonmail.com>