Support Document text detection

[dinosauria123]

When posting OCR request, we can choose two type of response.

A TEXT_DETECTION response includes the detected phrase, its bounding box, and individual words and their bounding boxes:

A DOCUMENT_TEXT_DETECTION response includes additional layout information, such as page, block, paragraph, word, and break information.

gcvocr.sh now uses TEXT_DETECTION. But it will change to DOCUMENT_TEXT_DETECTION to improve text quality.

[catabre]

I have raised the Pull request for the same.