fix warnings from rst2html

fix warnings from rst2html

Apparently the in-line link syntax with "<>" in them causes these warnings. I
don't know why. I changed them all to a slightly more verbose syntax.

Thanks to Mike Kazantzsev's review comment
(https://github.com/tahoe-lafs/tahoe-lafs/pull/67#commitcomment-4561370), I
moved the links to the end of each section.