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 thought so, but you changed line 90 to say, "the maximum possible hash value is 2**255".  Maybe that's the line which should be reverted.