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.
We originally used the term "generation transaction" but @mikehearn suggested we use "coinbase transaction".  I suggest we make sure both terms are introduced to help people searching based on a particular term but that we continue to use "coinbase" unless a discussion is held to change it.