Minor updates for readability improvements.

[ShararAwsaf]

Improvements include

• feistel.py

  • updated _xor to use the system specific byte order
  • included a split method for readability and to prevent repetition
  • changed round keys to lambda function instead of storing a list of keys
  • reverse traversal has been updated in decrypt method for readability

• encrypt.py

  • merged the encryption and decryption steps using an operation variable to avoid repetition

• iterators.py

  • fixed a minor is where the block size was set to constant 64

• utils.py

  • includes xor function as a cleanup process for modes.py

• modes.py

  • made changes to CBC and CTR to use utils and moved the mode specific variables for CBC to be included inside the CBC class instead