Better support for json-like input and outputs in the schema

[Coobaha]

Continuation of #89

request body is typed as json-like structure, while response body is not fully casted and doesn't cast original types from schema.

@qwelias, it was a nice puzzle! Could you please verify if it meets your expectations, works correctly, and covers all your cases? Thank you.

[qwelias]

Thanks a lot, will check out within a day

[qwelias]

looks great, thanks

[Coobaha]

@qwelias I released a @coobaha/[email protected] with this changes

I noticed one regression for undefined values in objects. I think it should make Jsonlike key optional, like:

type Obj = {
  a: string | null | undefined
}

type ResultJsonLikeType = {
 a?: string | null
}
declare const obj: Obj;

// works as JSON.strinigfy(obj) will remove undefined values
req.send(obj) // results in a {} response

#97