Allow for multiple subclasses which will be comma-delimieted

[jasonvan]

Example

|Room >> Kitchen color width height, Bedroom

• Interpreter will need to be updated to handle multiple main classes
• Encoders will need to be updated to handle multiple main classes

[jasonvan]

This work has been started in this commit: https://github.com/jasonvan/prexel/commit/f653dff13a3fe6b8e55d53ec0f139374dc219451

• [x] Need to address all TODOs inside of interpreter_redux.py and the test file
• [x] Need to create an XMI document or a more advances Diagram objects from the values inside of the evaluate method

[jasonvan]

Finished in this commit https://github.com/jasonvan/prexel/commit/c368207b0e921a444af46c17d0710d584d781c54