Add decoding functions and interface

[ajitzero]

This issue is for students who want to practice algorithms in Python.

Problem: Currently, the project lacks the option to decode a given string.

I also welcome code review from others since this was written entirely under an hour in my third semester.

Tasks:

• Add command-line interface to access decoding functions.
• Add decoding functions for every algorithm with necessary options.

Note: These are broad requirements, which will be dealt in separate pull requests and issues.