[FEATURE] Add a colored diff report

```phpcs --standard=Generic --extensions=php --report=coloreddiff --sniffs=Generic.WhiteSpace.DisallowSpaceIndent -vs CodeSniffer/Standards/Generic/Tests/WhiteSpace/DisallowSpaceIndentUnitTest.inc```

![coloreddiffoutput](https://cloud.githubusercontent.com/assets/363363/5558734/bf7d550e-8d32-11e4-9334-d29e477292d6.png)

@sascha-egerer this isn't a duplicate header. 1st one is File DocBlock, 2nd one is Class DocBlock. This is how it's done in all PHP_CodeSniffer PHP files. Yes, they are mostly identical, but usually short description is different.