switch to doing everything with full outDir/diagram.svg path

In other words, URLs will now look like <<outDir/diagram.svg#...>>,
and the entire output directory should be copied in alongside the
generated documentation.  This is to be consistent with the new
extra-html-files feature in cabal-install:

  https://github.com/haskell/cabal/pull/1182
link to README from description
make Setup.hs copy all SVG files in the diagrams dir, not just greenCircle
update documentation re: links to generated files
finish writing README