update links

[cblgh]

since i linked someone the dev portal i figured i'd put in a pr with some updated links! regardless of the future of things, i reckon it's useful if the current site is kept up to date. more concretely:

• ssb eu is defunct, so i removed that website and replaced it with a link to the documents repo of the ssb eu org
• glyph's solar repo has had significant work (457 additional commits, yowza!) compared to the linked kuska-ssb org (also defunct), so for rust i've linked to solar instead. you can still find kuska-ssb by the fact that solar is visibly forked from there