Added AstConstructor as a separate syntactic entity, which inherits from AstVariable similar to AstFunction.
Added a StructTest case
Fixes related to separation of AstFunction and AstConstructor
New systax for value construction T::A(). For this the AstExpressionConstruction was added. The rest is mostly generated,
Fixed new syntax plus *very* preliminary background type checking. Code gen does not work for tuples.
Quite a few changes to the grammar. A Major thing is that TypeRecord is replaced by TypeTuple, which may have one or more TaggedTuples (not a type). In addition a lot of clean ups and name changes in the grammar is done (AstTypeName is now called AstTypeUser). The code gen does not work. This check-in is a good point for Harald to see how the changes in the frontend and IR affects the code gen.