payload.Get(<path>) support ! -> . (dot) separated paths are now supported by payload.Get()

Support for . (dot) separated paths in the payload objects

Examples:

//convenient access
p.Get("address.street").String()

// indexed arrays
p.Get("address.options[0].label").String()

p := New(map[string]interface{}{
			"name":     "John",
			"lastname": "Snow",
			"address": M{
				"street": "jonny ave",
				"country": M{
					"code": "NZ",
					"name": "New Zealand",
				},
				"options": []M{
					M{
						"label": "item 1",
					},
					M{
						"label": "item 2",
					},
				},
			},
		})
		Expect(p.Get("name").String()).Should(Equal("John"))
		Expect(p.Get("address.street").String()).Should(Equal("jonny ave"))
		Expect(p.Get("address.country.code").String()).Should(Equal("NZ"))
		Expect(p.Get("address.options[0].label").String()).Should(Equal("item 1"))
		Expect(p.Get("address.options[1].label").String()).Should(Equal("item 2"))
	})