DevDocs corrections part 1

Started reviewing the developer docs, finding lots of things to correct. I'll do more later, but please review this batch first so I know what, if anything, needs to be fixed moving forward - I'm not entirely sure on the markdownish format used.
@luke-jr To your experience, the people commenting on the "Development and Technical" board, although not involved with Bitcoin Core, don't have a good technical understanding of Bitcoin? In any case, I have no strong opinion on this.