Rename `.u-*` to `.util-*`
Rename `.u-*` to `.util-*`

I'm using Skeleton (it's great!) in a project that also deals with microformats2, which specifies that `u-*` classnames are used to indicate url properties of machine readable markup.

Renaming `.u-*` to `.util-*` avoids this issue while potentially making it clearer that these are utility classes that apply inline styles.

Kevin Marks has a great detailed explanation of the issue here: http://www.kevinmarks.com/u-means-style.html
mkody/Skeleton