v1.1.1: fix MathJax \newcommand leakage

new fixes:
- http://meta.math.stackexchange.com/q/4130: The scope of \newcommand is the entire page
other changes:
- use @run-at document-start to allow early injection of MathJax config
v1.1.2: add position:relative to comments

new fixes:
- http://meta.stackoverflow.com/q/114109: Background in OP's user name can obscure text in multiline comments