Improve support of sub/superscript

![sub-super-strikethrough](https://cloud.githubusercontent.com/assets/1052079/3809642/8064f344-1c86-11e4-9597-eea9439d0b3d.png)


Test document: https://drive.google.com/file/d/0B1EH5OPb-RrjbW9DQ1VRLUxQUEE/edit?usp=sharing
Can do... it isn't completely vital though. If someone "improves" this and it breaks, the unit tests will fail, hence informing said developer that their improvement was a failure. I don't trust to comments what I can enforce with failing tests...