Speed up CS run by factor 4

[dereuromark]

We had some performance improvements done recently in Spryker
Our findings I also want to share with u.

Apparently, cs sniffer is > 4x faster without xdebug on.

23s => 10s for master branch since we dont have too many tests yet.

In larger code bases with even more sniffs this is quite noticeable:

• huge repo: 1470s => now only 319s (24 => 5 min!)
• medium repo: 118s => now only 26s (2 => 0.5min)

[dakota]

What also makes a huge difference is running it parallely (The --parallel option). We found a value of around 75 works really well (squizlabs/PHP_CodeSniffer#1732 for some more info)

[ADmad]

I guess the --parallel switch should be added in command used for core's travis job.

[swiffer]

@ADmad / @dereuromark - it's possible to define a cache file for PHP_CodeSniffer. This dramatically reduces runtime (48s -> 500ms)!

e.g. phpcs --cache=.cache/phpcs