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.
I think I prefer "generation transaction" and none of our images use the term "coinbase transaction" (I hate updating images because they create binary bloat in the repository), so I have no problems changing the term in the docs---except that two expert developers have each recommended against the term used by the other developer.

I suggest we revert the generation transaction changes in this pull and open a new pull that globally s/coinbase transaction/generation transaction/ (where appropriate with respect to code).  Then we can get this pull merged and try to solicit additional opinions from experts about terms on the new pull.