Update marked.js

adding support for ==highlight== and _underline_
oops, typo
Update marked.js
merged in solution for highlighting, as described [here](http://stackoverflow.com/questions/18213113/regex-exec-failing-to-match-string/18235347?noredirect=1#comment26744953_18235347) by kol
adding test for _ underline syntax
adding test for highlight
left some debug info, felt stupid
Merge branch 'b3n/master'

* b3n/master:
  left some debug info, felt stupid
  adding test for highlight
  adding test for _ underline syntax
  merged in solution for highlighting, as described [here](http://stackoverflow.com/questions/18213113/regex-exec-failing-to-match-string/18235347?noredirect=1#comment26744953_18235347) by kol
  Update marked.js
  oops, typo
  Update marked.js