PPX to generate typed TObj from records

[askvortsov1]

It should be possible to make a PPX that generates a function that maps an instance of some type "t" into the typed jingoo model representation. For projects with complex DB models, this could significantly cut down on boilerplate.

[tategakibunko]

Is it something like ppx_deriving_yojson? Certainly a ppx tool would be useful, but I don't know if it should be included in this package.