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.
Suggestions:

* s/a linear/in a linear/  (seems like the better usage)

* s/, on average,/ (on average)/  (I try to avoid comma-based parenthetical when other comma-based sentence divisions are being used)