UIView+RoundedCorners Category
by Warren Moore

Usage:
/* Round all corners */
[aView setRoundedCorners:UIViewRoundedCornerAll radius:8.0];
/* Round both left corners */
[aView setRoundedCorners:UIViewRoundedCornerUpperLeft | UIViewRoundedCornerLowerLeft radius:8.0];

Please note that using this method will create a mask layer for each UIView to which it is applied.
This may have severe performance implications. You are hereby advised to weigh the convenience of
this method against less elegant but substantially faster options.