Add "CombinatorRule"

[aik099]

The CombinatorRule would:

• accept:
  • array of rules as input
  • constraint (as all rules do)
• test method will:
  • call the test method on each of rules given in constructor
  • add +1 on each sub-rule match
  • use constraint to check count of matched sub-rules
• if not enough sub-rules matched then combine error messages from sub-rules using or (not sure this is best way to build error message)

P.S.

This proposal is far more easier to implement than one in #7.