ppx extension for rpclib

The library provides the [@@deriving rpc] ppx directly generates the conversion functions.

type t = ... [@@deriving rpc]

will give two functions:

• A function to convert values of type t to values of type Rpc.t : val rpc_of_t : t -> Rpc.t

• A function to convert values of type Rpc.t to values of type t : val t_of_rpc : Rpc.t -> (t,string) Result.result

It also supports the @key annotations for having different field names:

type t = { foo: int [@key "type"]; bar: int [@key "let"]; } [@@deriving rpc]