Render parameters and return discussion in jazzy

[jpsim]

Since these are now just markdown list items, this should be relatively easy. However, I had a really hard time figuring out the best way to do so in redcarpet, so this is something I could really use @segiddins's help with :wink:.

[jpsim]

The reason it'd be good to do this is to avoid relying on clang's/sourcekit's parsing of comment docs at all, whereas right now we're doing most of the work, other than these two items.

[segiddins]

Cool, should be able to spend some time pairing on this in the near future of you want