Username linking was disabled in
0f498d3ee3, leaving the test suite in a
failing state. This test can be restored when the functionality is
re-introduced.
brute forcing changes by regexps gets things wrong sometimes, so use
nokogiri to parse the html output of rdiscount and do changes on
individual nodes, then turn back into a string
we lose the ability to move punctuation inside of auto-generated
links, but i don't see any easy/definitive way to do this properly.
closes#242closes#209
