Convert hex to binary and binary to hex by slicing inputs & outputs into 4-bit nibbles

• Choose to which direction to convert
• Option to enter more conversions unless you quit

• 32-bit binary input
  Not really an issue, since you can simply change MAX_BITS_ALLOWED to allow infinite sequences of 0's and 1's

• Uses 2 dictionaries of 4-bit nibbles to convert both ways
• Robust error handling checks:
  • Binay input is <= 32 bits
  • Empty string input is correctly returns 0000 binary or 0 hex
  • Hex is converted to uppercase to avoid duplicate dictionary keys for lowercase
  • Binary input is validated to make sure it is only 0's and 1's
  • Hex input catches KeyErrors if the input is not a value 0-9 or A-F