Add support for app extension
Add support for app extension

xiaoyanit/DTCoreText,pivotaltracker/DTCoreText,Akylas/DTCoreText,rgregg/DTCoreText,Cocoanetics/DTCoreText,Cocoanetics/DTCoreText,openresearch/DTCoreText,Cocoanetics/DTCoreText,rgregg/DTCoreText,gnr/DTCoreText,Akylas/DTCoreText,programming086/DTCoreText