Added podspec; added to cocoapods

Hi Aaron

I created a release and a podspec. If you use it in cocoapods, it's current downloading from 
https://github.com/yichizhang/UIView-Borders.git

If you accept the pull request and create a 0.0.1 release, I can make it point to
https://github.com/aaronn/UIView-Borders.git