Add MakeResult(type Type, value ... interface {}) Result

[bjoerndemeyer]

I would like to be able to make Result types myself from non-json sources for use with Result.Less, etc, without having to use Parse(). Since Result's members are exported it's possible to construct it myself, but its is somewhat awkward and risks getting out of synch with this library. I am willing to provide aPR if this MakeResult seems a good idea. Or perhaps the name should be different.