std.manifestDebug

A function which takes any Jsonnet value and returns a string with all available information about the contents. It would be similar to `manifestJson`, but it would also:
(a) include hidden fields (with `::`).
(b) functions don't cause an error- instead functions are "serialized" to something like ``. We could also include argument names (but that is impossible from within Jsonnet).

Useful for debugging (analogues in other languages include Python's `repr`, Golang `go-spew` library and PHP `var_dump`).

Other possible names: `std.debug`, `std.dump`, `std.spew`.