Adds a simple but fairly complete UDT generator that generates POJOs that implement `SQLData` for mapping to PostgreSQL's composite types.
Highlights:
* Generates Java `class` POJOs for composite types
* Generates Java `enum` for enum types
* Handles types that reference other composite types/enums/arrays
* Can be called via CLI or as Java library
* Simple test suite that tests generated files for compilability.