HTML encode "registered trademark" symbols so they display properly

In both Internet Explorer and Chrome on Windows, the "registered trademark" symbols in the readme display as diamond question marks (see the screenshot. Is there a better name for those?)

HTML encoding the symbols seems to fix the issue.

![image](https://f.cloud.github.com/assets/516559/688399/842d68fa-da95-11e2-8b73-f1b4bd41cf78.png)