Block hash calculation

[tkstanczak]

Add block hash calculation:

BLOCK HASH A block hash is a hash of the block’s header elements.

Specifically:

pedersen_hash( parent_block_hash,block_number, new_global_root,sequencer, creation_time, transaction_commitment, transaction_count event_commitment, event_count, protocol_version, extra_data ) In StarkNet Alpha, each component that is not yet implemented is replaced with 0.

The code for the block hash generation can be found here.