Custom Forms (a few bug fixes)

This resolves an issue with the deployed 4.0 version that kept the drop down `.custom.dropdown.open.(small|medium|large) ul` from expanding beyond the width of the parent. The default behavior should be to let the drop down ul expand to the size of it's content. I also fixed a couple issues with the custom documentation.

![Screen Shot 2013-03-04 at 8 50 55 PM](https://f.cloud.github.com/assets/687594/219607/27b24494-8539-11e2-8106-3c5876f7845c.png)

I've discovered an issue as well. Because `em` sizing doesn't match exactly to pixels, there's some unpredictable offset issues. (notice the double-border in the following screenshot)

![Screen Shot 2013-03-04 at 8 50 48 PM](https://f.cloud.github.com/assets/687594/219615/55b813d2-8539-11e2-9060-3dd9da235db0.png)