Cast `getAvailableThreads` result to string in PHPCS arguments

Add configuration example (#7)

Bugfix release

Switch to `PHPCSStandards/PHP_CodeSniffer` as
`PHPCSStandards/PHP_CodeSniffer` is now unmaintained.

See #5

Merge pull request #4 from phpcq/feature/exec-plugin

Feature exec plugin

Bugfix release

Handle exclusions correctly

Initial release