docs: Add empty troubleshooting page
docs: Rename 'changes' to 'changelog'
docs: Reorganize frontpage sections
docs: Add empty 'contributing' page
docs: Tweak authors page
docs: Reduce depth of development ToC
docs: Updated intro
docs: Fix wording
docs: Add extension registry
docs: Move scrobbler docs to new ext registry
docs: Move HTTP to ext registry and API section
docs: Unbreak link from changelog
docs: Unbreak links from HTTP client page
docs: Move MPRIS to ext registry
docs: Move MPD to ext registry
docs: Unbreak links to MPRIS docs
docs: Move Spotify to ext registry
docs: Remove empty dummy backend docs
docs: Move stream to ext registry
docs: Move local to ext registry