sidestr-header 0.3.0

Block headers for sidestr sidechains, following the parent chain's family: the stock 80-byte SHA-256d header and Bitcoin Knots' 164-byte v2 header with the tagged-hash-plus-BLAKE2b proof of work, compact targets, powLimit checks and the BIP-325 block data; no_std, RustCrypto only. With the `core` feature, the sidestr-core HeaderFamily for both, so a BLAKE2b sidechain validates end to end. A port of bitcoin-desktop/schema and siding by Melvin Carvalho.