Write premisses instead of premissae
Wrap markdown output in valid HTML
Introduce references and specify their use
Pointer typedefs to forward declarations
Abstract base class for defined entities

These are entities such as types and variables.
Designed classes for predicates

We have declarations, definitions and anonymous definitions, all with
different characteristics. The class hierarchy encodes the relations
between these entities.
Used correct move semantics
Let quantifiers run over multiple variables

As we now, that doesn't change much, but it allows for shallower syntax
trees. And we can now use PredicateLambda directly.
Implemented functions to write predicates and co.

This includes writing quantifier and predicate expressions.
Wrote test along the lines of examples/simple.lth
Print test string