Color support [3.1]

[SebastianS90]

Squashed and cherry-picked #53 into 3.1

Can you merge this and tag it as 3.1.1? I cannot yet update to phpunit 6.0, so this would be helpful for me.

[gimler]

phpcov works with phpunit phpunit 5.7

[SebastianS90]

@gimler The latest 4.0.0 release of phpcov requires phpunit ^6.0, so it is not compatible with phpunit 5.7.
The latest 3.1 version of phpcov works with phpunit 5.7, but it does not include the patch from #53, therefore I cherry-picked it into the 3.1 branch.

[SebastianS90]

In the meantime, I updated my projects to current versions of phpcov and phpunit. So I no longer need this addition to phpcov 3.1. Since there seems to be no one else interested in this PR, I'm closing it.