Add abstract syntax

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Rename to closure

This is a much better fit for the specification's intention.

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Add utility module

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Add _build to ignore list

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Remove TODO

An assignment either assigns to a named reference or to
a tuple of expressions. Since tuples are part of the
syntax (but not of the semantics) of Modelica, we keep it
that way.

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Start a menhir parser

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Add parser/lexer framework

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>