Support for ColorGo

[kokizzu]

I'm using colorgo for coloring the compile output, it would be nice if gin support it too, for example with a certain flag -g or --go-command, for example:

gin -g /home/asd/Dropbox/go/bin/colorgo -i -b /tmp/test-build

[ianwalter]

Seems to be the same issue when using something like fatih/color to color log output. :rainbow:

[zh-h]

@ianwalter @kokizzu Look at my solotion https://github.com/zh-h/gin/commit/a621f6e0ed0a3c0d87a37323a6ecb02f97cd5c56