fix shard direction and remove obscur transpose

should close #2 (closed)

this MR

• uses the matrix representation of FEC encoding to create both Shards and Blocks
• 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