Add CLI Interface

[lycheeje11y]

A simple CLI interface for use on the command line...One thing to note is that I changed the argument in snake_to_camel to upper_case_camel from lower_case_camel...it still does teh exact same thing because to_lower_case_camel is defined later down to be the opposite of upper_case_camel. My reason for doing that it because that means the program would only end one flag for the is_constant and upper_case_camel. If I used the lower_case_camel, the program would need multiple flags, one for is_constant and one for lower_case_camel. Obviously, if you have a reason you want it to be lower_case_camel, you can ignore this PR. Thanks for reading!