BIP360: Pay to Merkle Root (P2MR) (#1670)

Review comments and assistance by:
  Armin Sabouri <armins88@gmail.com>
  D++ <82842780+dplusplus1024@users.noreply.github.com>
  Jameson Lopp <jameson.lopp@gmail.com>
  jbride <jbride2001@yahoo.com>
  Joey Yandle <xoloki@gmail.com>
  Jon Atack <jon@atack.com>
  Jonas Nick <jonasd.nick@gmail.com>
  Kyle Crews <kylecrews@Kyles-Mac-Studio.local>
  Mark "Murch" Erhardt <murch@murch.one>
  notmike-5 <notmike-5@users.noreply.github.com>
  Vojtěch Strnad <43024885+vostrnad@users.noreply.github.com>

Co-authored-by: Ethan Heilman <ethan.r.heilman@gmail.com>
Co-authored-by: Isabel Foxen Duke <110147802+Isabelfoxenduke@users.noreply.github.com>

bip-0360/ref-impl/rust/.cargo/config.toml

@@ -0,0 +1,2 @@
+[registries.kellnr-denver-space]
+index = "sparse+https://crates.denver.space/api/v1/crates/"