Create a Hill Cipher Class

This issue will mark the progress on the Hill Cipher.

Below are the various other items.

## The key setters.
### Tracked by issue #2
- [ ] Key Setters Tracked by issue

## Encryption/Decryption Methods
### Tracked by issue #3
The encryption method will include the sub-tasks of chunking the input into a decimal form based upon the index of each character of the input string. Encryption and decryption both share the same basic premise it's just that the encryption uses the encryption matrix whereas decryption uses the decryption matrix which is just the inverse of the encryption matrix.

- [ ] Encryption Method

Decryption method including converting the
- [ ] Decryption method

## I/O Methods Issue
### Tracked by issue #4
- [ ] Write data to a file.
- [ ] Read data from a file.

## Known Plaintext Attack
### Tracked by issue #5
- [ ] Using the crib by search for the data.
- [ ] having a sliding window across the input data to attempt to find the data.

## Unit Tests
### Tracked by issue #6
- [ ] Encrypting test vectors
- [ ] Decrypting test vectors
- [ ] KPA test vectors.

## Driver Program
### Tracked by issue #7
- [ ] The basic Driver Program
- [ ] Prompt user for input alphabet.
- [ ] Prompt user for the input key(or generate one itself)
- [ ] Allow command line arguments.
- [ ] Read in data from a file to do KPT through the menu by prompting for file. Or automated via the command line argument.
- [ ] Setup a basic menu for the whole thing.

This is a large, multi-part feature to implement a Hill cipher class with encryption, decryption, file I/O, known-plaintext attack, unit tests, and a driver program. The issue is a tracking issue referencing other issues for subtasks. A newcomer would need to understand the Hill cipher algorithm, linear algebra for matrix inversion, and C++ class design. Start by reading the linked issues (#2-#7) to understand the scope of each component. The driver program suggests a command-line interface. 'Done' means a complete, tested class with all listed functionality.

索引モデルが issue の本文から書いたものです。