Hi all,

        There have been a number of suggested changes to the commitment
transaction format:

1. Rather than trying to agree on what fees will be in the future, we
   should use an OP_TRUE-style output to allow CPFP (Roasbeef)
2. The `remotepubkey` should be a BIP-32-style, to avoid the
   option_data_loss_protect "please tell me your current
   per_commitment_point" problem[1]
3. The CLTV timeout should be symmetrical to avoid trying to game the
   peer into closing. (Connor IIRC?).

It makes sense to combine these into a single `commitment_style2`
feature, rather than having a testing matrix of all these disabled and

BOLT #2:

- If `commitment_style2` negotiated, update_fee is a protocol error.

This mainly changes BOLT #3:

- The feerate for commitment transactions is always 253 satoshi/Sipa.
- Commitment tx always has a P2WSH OP_TRUE output of 1000 satoshi.
- Fees, OP_TRUE are always paid by the initial funder, because it's simple,
  unless they don't have funds (eg. push_msat can do this, unless we remove it?)
- HTLC-timeout and HTLC-success txs sigs are 
- `localpubkey`, `remotepubkey`, `local_htlcpubkey`,
  `remote_htlcpubkey`, `local_delayedpubkey`, and `remote_delayedpubkey`
  derivation now uses a two-stage unhardened BIP-32 derivation based on
  the commitment number.  Two-stage because we can have 2^48 txs and
  BIP-32 only supports 2^31: the first 17 bits are used to derive the
  parent for the next 31 bits?
- `to_self_delay` for both sides is the maximum of either the
  `open_channel` or `accept_channel`.
- `to_remote` is now a P2WSH of:
        `to_self_delay` OP_CSV OP_DROP <remotepubkey> OP_CHECKSIG


[1] I recently removed checking this field from c-lightning, as I
    couldn't get it to reliably work under stress-test.  I may just have
    a bug, but we could just fix the spec instead, then we can get our
    funds back even if we never talk to the peer.
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