Enhance output

In addition to my other PR I made some more enhancements.

First one is to increase windows support. Sadly the windows terminal doesn't support unicode, so the success and failure icons aren't correctly displayed. I changed them to simple `+` and `-` signs.

Second one is colorized output. I added some colors to make the output more pretty.

Third one is failure display. On occurence of a failure, there was shown a stack trace which wasn't very useful. I changed it to display the code of the failed test instead.

Note: this PR depends on my other #1