Revises testdata structure some more.
Further work on imlpementing assembler and related unit tests.
implements more unit tests for AST and Assembler.
Applies some bug fixes to Assembler and AST/Lexer.
Finalizes resolution of references and verification of
their existence. Additionally reformats the AST to give
each definition and reference a fully qualified name.

E.g.: Function 'F' in package 'foo/bar', will be renamed
to 'bar.F'.

Label 'loop' inside this function will become 'bar.F.loop'.
The same goes for constant definitions.