Research: Using Bitcoin::Crypto to verify the blockchain

[bbrtj]

The module may be at the stage where we can start thinking about verifying Bitcoin blockchain with it, starting with the genesis block up. Of course this won't work out of the box, even if we assume a library for connecting with other node was already written. To keep it simple we can fetch raw blocks from Bitcoin Core. This needs research and more additions to Bitcoin::Crypto. I'm looking for people willing to look into it.

List of tasks to do is sure to contain:

• verifying blocks as a whole
• calculating target difficulty of blocks (proof of work)
• tracking consensus changes (versionbits, super majority, etc) and activating transaction validation flags
• storing UTXOs away from memory
• adding a rule for coinbase transaction output to only be spendable after 100 blocks
• possibly more

[bbrtj]

A lot of work on performance has been done to ensure this can be completed before the heat death of the universe. Next version (most likely 4.003) will be well over 2 times faster at deserializing and verifying transactions than 4.002. Added a note in the docs with a list of optional modules that should be installed for best performance.