Fixed existing javadoc, added missing @Overrides

This pull request in general fixes up Javadoc for missing params, broken links, returns on voids, and similar things. It also includes Javadoc on some things that did not previously have it. I would have done more, but for some things I wasn't sure about your specific thoughts on how it should work so I left it as is.

I'm rather tired as it's 12:30 right now and I normally go to bed at 10, so let me know if anything needs to be fixed or you want more description of the PR or something, as I may have missed it.
BEFORE_POST and POST were supposed to be no-cancel and read-only stages.  There was another commit that fixed the typo.