Shortcut syntax idea

Just an idea and working code.
Added `have` matcher. It accepts path and type. Type is not required.
Symbol will be interpreted as Integer and a string as String
Examples:
```ruby
json = normalize_json(last_response.body)

# json.should have_json_type(Integer).at_path('id')
# can be written as
json.should have :id
# or
json.should have :id, Integer

# json.should have_json_type(String).at_path('first_name')
json.should have 'first_name'

# any defined class
json.should have :my_float, Float
json.should have 'my/flag', TrueClass
```