v0.0.100

API Updates

• The lightning crate can now be built in no_std mode, making it easy to
  target embedded hardware for rust users. Note that mutexes are replaced with
  no-ops for such builds (#1008, #1028).
• LDK now supports sending and receiving "keysend" payments. This includes
  modifications to lightning::util::events::Event::PaymentReceived to
  indicate the type of payment (#967).
• A new variant, lightning::util::events::Event::PaymentForwarded has been
  added which indicates a forwarded payment has been successfully claimed and
  we've received a forwarding fee (#1004).
• lightning::chain::keysinterface::KeysInterface::get_shutdown_pubkey has
  been renamed to get_shutdown_scriptpubkey, returns a script, and is now
  called on channel open only if
  lightning::util::config::ChannelConfig::commit_upfront_shutdown_pubkey is
  set (#1019).
• Closing-signed negotiation is now more configurable, with an explicit
  lightning::util::config::ChannelConfig::force_close_avoidance_max_fee_satoshis
  field allowing you to select the maximum amount you are willing to pay to
  avoid a force-closure. Further, we are now less restrictive on the fee
  placed on the closing transaction when we are not the party paying it. To
  control the feerate paid on a channel at close-time, use
  ChannelManager::close_channel_with_target_feerate instead of
  close_channel (#1011).
• lightning_background_processor::BackgroundProcessor now stops the
  background thread when dropped (#1007). It is marked #[must_use] so that
  Rust users will receive a compile-time warning when it is immediately
  dropped after construction (#1029).
• Total potential funds burn on force-close due to dust outputs is now limited
  to lightning::util::config::ChannelConfig::max_dust_htlc_exposure_msat per
  channel (#1009).
• The interval on which
  lightning::ln::peer_handler::PeerManager::timer_tick_occurred should be
  called has been reduced to once every five seconds (#1035) and
  lightning::ln::channelmanager::ChannelManager::timer_tick_occurred should
  now be called on startup in addition to once per minute (#985).
• The rust-bitcoin and bech32 dependencies have been updated to their
  respective latest versions (0.27 and 0.8, #1012).

Bug Fixes

• Fix panic when reading invoices generated by some versions of c-lightning
  (#1002 and #1003).
• Fix panic when attempting to validate a signed message of incorrect length
  (#1010).
• Do not ignore the route hints in invoices when the invoice is over 250k
  sats (#986).
• Fees are automatically updated on outbound channels to ensure commitment
  transactions are always broadcastable (#985).
• Fixes a rare case where a lightning::util::events::Event::SpendableOutputs
  event is not generated after a counterparty commitment transaction is
  confirmed in a reorg when a conflicting local commitment transaction is
  removed in the same reorg (#1022).
• Fixes a remotely-triggerable force-closure of an origin channel after an
  HTLC was forwarded over a next-hop channel and the next-hop channel was
  force-closed by our counterparty (#1025).
• Fixes a rare force-closure case when sending a payment as a channel fundee
  when overdrawing our remaining balance. Instead the send will fail (#998).
• Fixes a rare force-closure case when a payment was claimed prior to a
  peer disconnection or restart, and later failed (#977).

Serialization Compatibility

• Pending inbound keysend payments which have neither been failed nor claimed
  when serialized will result in a ChannelManager which is not readable on
  pre-0.0.100 clients (#967).
• Because
  lightning::chain::keysinterface::KeysInterface::get_shutdown_scriptpubkey
  has been updated to return a script instead of only a PublicKey,
  ChannelManagers constructed with custom KeysInterface implementations on
  0.0.100 and later versions will not be readable on previous versions.
  ChannelManagers created with 0.0.99 and prior versions will remain readable
  even after the a serialization roundtrip on 0.0.100, as long as no new
  channels are opened. Further, users using a
  lightning::chain::keysinterface::KeysManager as their KeysInterface will
  have ChannelManagers which are readable on prior versions as well (#1019).
• ChannelMonitorUpdates created by 0.0.100 and later for channels when
  lightning::util::config::ChannelConfig::commit_upfront_shutdown_pubkey is
  not set may not be readable by versions prior to 0.0.100 (#1019).
• HTLCs which were in the process of being claimed on-chain when a pre-0.0.100
  ChannelMonitor was serialized may generate PaymentForwarded events with
  spurious fee_earned_msat values. This only applies to payments which were
  unresolved at the time of the upgrade (#1004).
• 0.0.100 clients with pending Event::PaymentForwarded events at
  serialization-time will generate serialized ChannelManager objects which
  0.0.99 and earlier clients cannot read. The likelihood of this can be reduced
  by ensuring you process all pending events immediately before serialization
  (as is done by the lightning-background-processor crate, #1004).

In total, this release features 59 files changed, 5861 insertions, and 2082
deletions in 95 commits from 6 authors.