This is also taken and adapted from lightningd/bitcoind.
The call to 'getblockchaininfo' is replaced by 'echo' as we don't
make use of the result and the former can sometimes be slow (e.g. on
IBD).
Most is taken from lightningd/bitcoind and adapted. This currently
exposes 5 commands:
- `getchaininfo`, currently called at startup to check the network and
whether we are on IBD.
- `getrawblockbyheight`, which basically does the `getblockhash` +
`getblock` trick.
- `getfeerate`
- `sendrawtransaction`
- `getutxout`, used to gather infos about an output and currently used by
`getfilteredblock` in `lightningd/bitcoind`.
darosior