Updates Throughout

New additions:

• Implemented java and python executors.
• Properly auto-detect executor based on file extension.
• Allow customisation of stdin and stdout filename.
• Have a default output directory path.
• Defaults to 5 testcases if no subtask is specified.
• Always use unix \n newline for output files.

Breaking changes:

• Refactor core module. It is now split into generator, resolver and subtask.
• Rename class from VarRef to ValueRef
• Rename class from RandomItem to RandomChoice
• Rename generator attribute ouput_dir to output_directory.
• Remove generally useless generator.repeat method.
• Remove executor attribute from generator class.

Other changes:

• Improve generation speed with various string concatenation improvements.
• Optimised imports.
• Add various checks and validation.

There is now an RTD site for this lib: https://testcase-maker.readthedocs.io/en/stable/