Some refactoring done ...

Also added a new folder "Change notes" in the project directory, to put
our change logs in

• Renamed class BullsAndCowsNumber to SecretNumber
• Added access modifiers where they were absent. Example:
char[] cheatNumber => private char[] cheatNumber
• Added a private backing variable (field) for each public property
• Converted shortened properties to their full form
• Introduced constant MAX_CHEATS_COUNT
• Renamed rrr to randomGenerator
• Renamed cheats to cheatsCount
• Reformatted the switch block in GetCheat() method