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.
"coinbase transaction" is 3.5 times more used according to Google than "generation transaction" and merging the current pull request would make us inconsistently use both terms, so indeed I think we should revert this and open a seperate pull req so this doesn't block all other useful changes (if @luke-jr doesn't have time, I or @harding could revert this before merging).