initial implementation of set operators
add containsSubset Operator
add case insenstive string comparison
Merge remote-tracking branch 'ludicruz/develop' into feature/set-operators

Conflicts:
	src/Ruler/Operator/SetContains.php
	src/Ruler/Operator/StringContains.php
	src/Ruler/Value.php
Minor coding standard fixes.
Refactor RuleBuilder set operator methods

Extract common functionality into private helper method.
Update docblocks for Set.
Restore Contains operator, but deprecate it.

Defer to StringContains or SetContains, trigger an E_USER_DEPRECATED with a helpful message.