Add groupBy() for matching

[danon]

Allow certain match() methods to return grouped values.

Methods:

• groupBy(string|int) - groups by capturing group
• groupByCallback(callable) - groups by user defined callback

Requirements:

• All of them must be usable with filter()->groupBy().

Example for all()

pattern('\d+(?<unit>cm|mm)')->match('12cm 14mm 13cm 19cm 18mm 2mm')->groupBy('unit')
  ->all();

[
  'cm' => ['12cm', '13cm', '19cm'],
  'mm' => ['14mm', '18mm', '2mm']
]