Reorg and document

[eagmon]

This PR is a major reorganization of the repository, but maintains the same functionality.

• The type functions are now organized in their own file type_functions.py, in which they are sorted by their function type (apply, divide, serialize, etc), and extended docstrings are included.
• Removes the dependence on loading unit types directly into a core, and instead makes a units_type dict like the other type dicts.
• removes the empty data file, which was used for building the dataclass. instead this module is dynamically created.
• removes unused react.py file.
• a new utilities.py includes the functions that were getting reused between different modules, simplifying the import structure to avoid circular imports.