Added color to pass/fail output

Not sure if you'd be interested in this, but I added color to the output for my own purposes. Color is set by MINUNIT_FAIL_COLOR and MINUNIT_PASS_COLOR which default to red and green respectively. The reset value to is to turn output back to the original color after printing.

I'd prefer if this were an option set by a flag, but I can't think of a good way to do so.

![](http://i.imgur.com/ovOnyjv.png)