Adds 'parallel' option support to phpcs task.

[mrmishmash]

Q	A
Branch	master for features and deprecations
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Documented?	yes
Fixed tickets	comma-separated list of tickets fixed by the PR, if any

This change adds support for 'parallel' option for the phpcs and phpcbf fixer. By default the option is set to null, which means it
runs normally, if it's a positive integer that's the number of processes that will be used. If 'auto' is used the number of processors on the machine will determine the number.

New Task Checklist:

• Are the dependencies added to the composer.json suggestions?
• Is the doc/tasks.md file updated?
• Are the task parameters documented?
• Is the task registered in the tasks.yml file?
• Does the task contains phpunit tests?
• Is the configuration having logical allowed types?
• Does the task run in the correct context?
• Is the run() method readable?
• Is the run() method using the configuration correctly?
• Are all CI services returning green?

[veewee]

Lookin' good!
I do have a remark about the auto CPU detection

[mrmishmash]

Yeah I was also thinking about this, it just adds complexity to the task and there also wasn't a straightforward way to test it. Good point that this should be done in phpcs.

In any case developers can add detection of the number of cores in their build processes and set it as the value for the 'parallel' option.

So with that in mind I have removed the auto detection of the cpu cores. Thank you for the input.

[veewee]

Thanks!