Remove default max-width from images

This just overrides one tiny setting in Bootstrap, and the result is images can be wide than the post width:

![screen shot 2013-06-26 at 9 43 27 pm](https://f.cloud.github.com/assets/254753/713590/fb1d4916-ded3-11e2-8e2f-7df8423b2261.png)