cleanup and documentation

Note
this MR is best reviewed commit by commit, it's hopefully clear enough.

Note
waiting for !47 (merged) to land

changelog

• add missing format to the KomodoErrors
• rename fec::Shard::bytes to fec::Shard::data because these are no bytes
• rename the blocks: Vec<Shard<E>> argument of fec::decode to shards
• refactor the tests of fec and lib.rs
• remove the batch_verify function entirely as it's pretty useless
• simplify the linalg::Matrix::random function
• add tests for the function in the setup module
• add documentation where it was missing