New grammar for handling declarations in a more SML-ish fashion.
Changes to parse decl. sequences, both inside let and at top-level
Handle conversion to Asts of top-level decl. sequences.
Make tests fail if ast-conversion doesn’t give back an answer.
Complete handling of declaration sequences and semi-colons therein.
Use EVAL to check parse-tree validity (much faster).

Have to rewrite some theorems to get rid of existential quantifiers
and use various destructors instead.