vision API manual detection documented but not implemented

[ptone]

https://github.com/GoogleCloudPlatform/google-cloud-python/blob/master/docs/vision-usage.rst#manual-detection

wah?

https://github.com/GoogleCloudPlatform/google-cloud-python/blob/master/vision/google/cloud/vision/image.py#L88

documentation written by @daspecster
95a55c1

[daspecster]

@ptone, sorry about that. There was a lot of froth in deciding the surface and this slipped by me.

In the meantime you can use client.annotate to do multiple detections. I will get a PR to correct this ASAP!