Minimum viable Bitcoin RPC support

[Fang-]

This includes a bitcoin sur and lib for dealing with Bitcoin RPC requests and responses.
I've included a simple /app/bitcoin-cli that uses the lib to forward RPC call nouns to an actual node. Very bare-bones, with hard-coded URL and all... but it works!

This PR is easily considered incomplete, but I'm opening it for discussion to support further development. Maybe we're fine merging this as-is though? It works, and "support additional Bitcoin RPC calls" might be a good contributor issue.

It'd be cool if we could send transactions in whatever way. I think my best bet it to talk to @loganallenc about what the deal is with the accounts/wallets and transactions interfaces.
I vaguely remember there being auras for bitcoin addresses, does anyone know what they are?

The request-tag-as-json-id pattern here feels pretty nice. We might want to consider using that for Ethereum RPC integration as well, as a default, but I haven't thought it over much yet.

Includes/depends on #1051.

[dpc]

I wish I could understand the code more, but hoon is still new and foreign to me.

From what I can deduce - this will require running a bitoin core node locally? And the plan is to use bitcoin core's wallet API to manage keys etc.? I wish urbit could do bitcoin crypto internally, and create addresses in hierarchical-deterministic fashion, and then craft transactions. Then it could be configured even against a (set of) remote node, or be an SPV wallet.

I'm looking forward to trying this out.

[Fang-]

this will require running a bitoin core node locally?

This will require RPC access to any node. It doesn't need to be local. But I got the impression (from hasty searches) that public RPC-enabled nodes aren't at all common in Bitcoin?

I wish urbit could do bitcoin crypto internally

Generating and signing raw transactions seemed too complicated for MVP work (you need to manually specify inputs and outputs? I haven't looked into this too deeply either), but I do definitely want to support the "wallets on urbit" case. We already have ECDSA, BIP32 and BIP39 implementations, so most of the groundwork is out of the way. It's just a matter of applying that to actual transactions.

I think you might still need at least a local light node in that case, unless I'm wrong about the public RPC nodes thing. (There's probably also services offering plain ol' web APIs, but those aren't as interesting.)

[Fang-]

(I'd be happy to talk you through the code, by the way. It's really quite dumb. Feel free to get in touch over email while chat is down.)

[dpc]

I've shoot you an email @Fang- . TTYL

[jtobin]

This PR is easily considered incomplete, but I'm opening it for discussion to support further development. Maybe we're fine merging this as-is though? It works, and "support additional Bitcoin RPC calls" might be a good contributor issue.

As I pass through the list of open PRs, wearing my finest hooded black robe and carrying my favourite nine-foot scythe, I note that this one could probably be closed for the time being, my good man.
Discussion has slowed down on it without really going anywhere, and as you point out, it could probably stand to bake a bit more anyway.

Yea / nah?

[Fang-]

Yeah very fair. I will return!