Footnote based doc embedding

[pnkfelix]

niko points out that embedding the documentation into comments directly in place (as is currently done in tango) breaks up the flow of the code significantly. When you're looking at the .rs file, you probably want to focus on the code itself, not the documentation.

One way to deal with this would be to stop embedding each block of documentation into a comment at that place, and instead emit a comment that just references a footnote. And then emit all the documentation, with the footnotes, at the end.