Implement Roles

[timjen3]

This can't be done until after #103 is complete ✅

Some details about Roles:

• Roles will serve as templates for building entities.
• Contain a list of attributes with metadata related to each one. Such as valid ranges of values
• Would be cool to be able to "sub-class" Roles. Subclass would get all attributes from parent with the ability to override some. Would be useful for relationships like Lifeform => Human => Fighter.
• A factory can build an entity from a role definitions.
• Add a parser to build an entity according to a command.

Entities should be supplemented with data from roles like:

• derived attributes; these don't contain values but formulas for calculating values. the derived attributes live on the role but are available to the entity
• categories should live on the role, not on the entity.