ENH: Update CornerAnnotation extension

This updates the CornerAnnotation extension to
0b381ea5a9d634e721f3e3acb731f3b5417f7658.
Merge pull request #771 from ayamada0614/update-CornerAnnotation-master

ENH: Update CornerAnnotation extension
ENH: Update CornerAnnotation extension

This updates the CornerAnnotation extension to
871e9798adc1e65ead54f33bc2ac758e518eedcd.
Merge pull request #772 from ayamada0614/update-CornerAnnotation-master

ENH: Update CornerAnnotation extension