Move assessments to analyses and more

[chalin]

• Followup to #229
• Moves:
  • assessments to analyses
  • assistance.md → docs/assistance.md
• Link-checks more files under docs
• Fixes issues reported by the link checker
  • Ignores (temporarily) in-page links since those are failing
• Some spelling corrections, but I've disabled the spell-checker until the pages are reformatted (in a follow up PR).