Modern Dokka

[FWDekker]

Modernises the Dokka setup:

• Adds a version dropdown menu to switch between versions.
• Adds a workflow that will update the GitHub pages automatically when a new GitHub release is created.
• Adds an icon and favicon to the documentation.
• Fixes a bug where the version number is displayed multiple times in the header.
• Shows documentation for all functions, not just public functions. (I think I've "fixed" this bug multiple times over the years...)

In the process, I also discovered and reported Kotlin/dokka#3398.

Also, rewrites the security policy. The most relevant change here is that vulnerabilities should preferably be reported through GitHub's reporting system instead of mailing it to a private email address. (Though I will still see emails to the old address.)

Also bumps a few dependencies.

[codecov]

Codecov Report

Merging #505 (a7a7756) into main (dd6ca0e) will increase coverage by 0.04%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #505      +/-   ##
==========================================
+ Coverage   85.04%   85.09%   +0.04%     
==========================================
  Files          52       51       -1     
  Lines        1993     1992       -1     
  Branches      335      335              
==========================================
  Hits         1695     1695              
+ Misses        235      234       -1     
  Partials       63       63