Unify Json and Ppx_deriving_runtime

[jchavarri]

Idea by @andreypopp (pls explain more deets if you think I'm missing): Unify Json and Ppx_deriving_runtime modules.

Upside: Shorter name, easier to find.
Downside: might lead to larger JavaScript bundles for people not using the PPX.

To mitigate the downside, maybe we could create a new Melange_json module that includes both? I have always thought that the top level Json module is a bit presumptuous.

cc @anmonteiro

[andreypopp]

Thanks for opening the issue, @jchavarri. So yeah, I propose to make a single lib which is usable both by user-written code and function as a runtime lib for ppx.

There's already a big overlap between the Json and Ppx_deriving_json_runtime so people who use both now — will have code duplicated in the bundle. So essentially I propose to dedupe code.

Another advantage is that Ppx_deriving_json_runtime now works for code which is compiled both to native and to melange and besides encoding/decoding it also provides functions to parse JSON, classify JSON (useful for custom decoding). So I think Ppx_deriving_json_runtime is useful standalone (without ppx) but is awkward to use because of its name.

At the same time, I agree with @jchavarri that the chosen Json name is too presumptuous, I like Melange_json.

[andreypopp]

I think this also addresses #9

[davesnx]

I think JSON is nice ^^