[React] proptypes-parser: Define React PropTypes with readable string.

``` const propTypes = parsePropTypes(`{ number: Number string: String! boolean: Boolean function: Function! date: Date! object: Object! shape: { nested: Number array: [Number] must: Boolean! }! array: [Number!]! arrayOfObjects: [{ value: String }!] node: Node element: Element! message: Message! any: Any! }`); ```

is equivalent to:

``` const propTypes = { number: PropTypes.number, string: PropTypes.string.isRequired, boolean: PropTypes.bool, function: PropTypes.func.isRequired, date: PropTypes.instanceOf(Date).isRequired, object: PropTypes.object.isRequired, shape: PropTypes.shape({ nested: PropTypes.number, array: PropTypes.arrayOf(PropTypes.number), must: PropTypes.bool.isRequired, }).isRequired, array: PropTypes.arrayOf( PropTypes.Number.isRequired, ).isRequired, arrayOfObjects: PropTypes.arrayOf( PropTypes.shape({ value: PropTypes.string, }).isRequired ), node: PropTypes.node element: PropTypes.element.isRequired, message: PropTypes.instanceOf(Message).isRequired, any: PropTypes.any.isRequired, }; ```