Bolt 12 support

[Sjors]

In order to support BOLT 12 offers - for single as well as recurring - I suggest adding one or two fields to the JSON:

1. bolt12_single
2. bolt12_recurring

The best practice then would be to create two offers, without an amount. Like so in c-lightning:

lightning-cli offer any "Open source development donation" "Shady Super-Coder" "open-source-single-donation"
lightning-cli offer any "Open source development monthly donation" "Shady Super-Coder" "open-source-monthly-donation" null null null 1month

The site could then display these somewhere (as plain text for now, QR when mobile wallets support it).

On the donator side IIUC they use lightning-cli createinvoicerequest [bolt12]. This method is as yet undocumented, so yolo. I assume it returns an invoice that you then pay.

There's some discussion about making this flow more automated: lightning/bolts#798 (comment)

Initially perhaps bolt12_single is a good start, since recurring payments are very tedious. But they would be really awesome once there.

[renepickhardt]

Concept ACK

[Sjors]

Fwiw, I actually received a donation this way: https://twitter.com/rusty_twit/status/1420565586552057862

[dennisreimann]

@Sjors Can you open a PR with those properties added for your profile? I can take care of displaying that info then :)

[Sjors]

@dennisreimann thanks! Done in #104

[dennisreimann]

I think the UX or at least description can be improved, but let's go with this as a start …

[Sjors]

Nice! A distinction between fiat and lightning could make sense, maybe just add $ and a lightning bolt.