1. Deleting Crop and CropPad functions
2. Moving I420Mirror to planar functions
3. deleting general.h and general.cc
Review URL: http://webrtc-codereview.appspot.com/269008

git-svn-id: http://libyuv.googlecode.com/svn/trunk@67 16f28f9a-4ce2-e073-06de-1de4eb20be90