fix shard direction and remove obscur transpose (dragoon/komodo!26)

should close #2 

this MR
- uses the matrix representation of FEC encoding to create both `Shard`s and `Block`s
- `fec::encode` will encode shards with a Vandermonde matrix
- `encode` will use `fec::encode`
- use of `Matrix::transpose` has been reduced in `fec::encode` thanks to swapping the encoding matrix product (thanks @j.detchart for findind this)
- `fec::encode` does not require `transpose: bool` anymore as the encoding process has been homogenize throughout the code base
- useless `field::build_interleaved_polynomials` have been removed
- `prove` has been merged into `encode`