A function to return segmented image

[changbaishan]

Segmented image can be displayed with vis_semantic_segmentation function. It can be saved as a result. What I suggest is a separate function that can return the segmented image directly. This image can be saved by users directly. This way, users can better use chainercv. thank you.

[knorth55]

thank you for the feature request.
you want a function to save evaluation visualization image.
i think it is a good function for headless environment such as cluster server.

[changbaishan]

Thank you knorth55.