Add demo

[xingyizhou]

Hi, Here is a demo script for CornerNet. It visualizes the output given an image path or an image folder path, by running python demo.py --demo /path/to/image/or/folder. The first commit only shows the detection results, and the second commit supports visualizing the heatmaps.

[JoJoliking]

It's a excellent prgramme

[hx358031364]

inp_height = new_height | 127

What would you like to add “|” ， 127？