Documented more functions to BlockchainDB, but I removed the ones that strictly concern
the database. These methods will be implemented under KeyValueDatabase trait.
Still needs to understand some things before starting to refactor blockchaindb functions.
Also enabled derive features for serde.
Removed some functions that'll be useless for blockchainDB. Docs the hardfork info ones.
Also set clippy to deny `expect()` and `panic!()` as /u/danda suggested on reddit.
Set blockchain_db in workspace dependencies + corrected the build rustflags.
