Migrate docs to gi-docgen (Take 2)
The hotdoc documentation system in use is lately falling somewhat behind in terms of maintenance. Make a second try at porting to gi-docgen. While at it many small improvements were done:
- API docs have been further fleshed up
- Documentation in general makes better use of consistent terms (e.g. RDF triple store)
- Sections have been refurbished to make better use of the navigation sidebar
- Class hierarchy ascii art was replaced with fancy SVGs with linked items
- There's now more diagrams for relations between RDF classes
Hopefully that makes docs nicer to read and navigate around.