Only this way it's possible to include the original standard in own
phpcs configuration.

* As we can use returns instead of local variable.
* This will make it easier to see the return value of the method.

* Do not use else, as hinted by phpmd, use return instead.

* Remove duplicate empty line.
* Sort namespace imports alphabetical.

Readded old composer package type `php-codesniffer-standards`.
Will be removed before the first stable release.

Added `phpcodesniffer-standards` (plural) as also supported
composer package type.

As requests in #24 i renamed the primary composer plugin type
from `php-codesniffer-standards` to `phpcodesniffer-standard`
for compatibility reasons to other projects.