feature: generics

[gijsvcuyck]

Implement generic type definitions for TorXakis

• Add generic type definitions.
• Implement new typing rules for generic types.
• Update existing type system to handle generic types.
• Allow defining functions over generic types
• Create analyzer that checks for each generic type with which concrete types it has been initialized.
• Create analyzer that checks for each generic function with which concrete types it has been called.
• Create generator that uses results of analyzers to generate non-generic instances of all generic types and functions as needed.