Start development series 0.5.x
Restrict P array to only non-zero even length sequence
Remove unnessasry bytes conversion of `key`.
Clearify comments
Inline L, R swap in _cycle_fast by looping over P in pairs of two.

This leads to two optimizations. First, the overhead of swap is removed and
the for loop is now half the size.
Also set local P array to the tuple version to speed up encryption locally
Seperate tests and benchmarks into seperate files.
Inline all encryption in Cipher.__init__
Inline cipher encryption rounds in encrypt_block
Inline decryption rounds in decrypt_block
Inline encryption rounds in encrypt_ecb
Inline decryption rounds in decrypt_ecb
Inline encryption rounds in encrypt_cbc
Inline decryption rounds in decrypt_cbc
Inline encryption rounds in encrypt_pcbc
Inline decryption rounds in decrypt_pcbc
Inline encryption rounds in encrypt_cfb
Inline decryption rounds in decrypt_cfb
Inline encryption cycles in encrypt_ofb and by extension decrypt_ofb
Inline encryption rounds in encrypt_ctr and by extention in decrypt_ctr