Update bitcoin dependency

[jrawsthorne]

Updating to the latest rust-bitcoin version brings some nice features such as the new hash types

In order to do this hammersbald needs to be updated (rust-bitcoin/hammersbald#13)

There also needs to be a decision about lightning.

• The latest rust-lightning release was in April and doesn't use the latest version of bitcoin.
• The module doesn't even compile currently
• Most of the interfaces rust-lightning requires aren't provided by this library yet

I propose we remove the lightning module for now until the core functionality is finished

[TheBlueMatt]

That seems fine to me, certainly anyone doing the work to maintain murmel can do whatever is easiest. rust-lightning will likely update to latest rust-bitcoin soon, we'll need to bump rust-secp and bitcoin_hashes as soon as a new release is cut either way.