Add containJson argonaut matcher

[stacycurl]

{a: 1, b: 2, c: { d: 3 } } should containJson {a: 1, c: {d: 3}}

{a: 1, b: 2, c: { d: 3 } } should beIdenticalTo {a: 1, c: {d: 3}} ignoringNot("/a, /c/d") where the paths are derived from the expectation.