Renamed files.
Major improvements to the parser.

Now AST is enriched with position info for better
error messages.
Much better type checking for NIL.
Much better runtime error handling.

We now emit the line number where the error occurred.
Improved type system design.

We got rid of polymorphic array type (TIGanyarray).
Made parser ocamlyacc-compatible.

Also we now record the location of syntax errors.
Improved typing system.

- recursive types now work correctly.
- needs to work a little in error reporting of
  non-existent types.
- needs to report an error if a type is defined more than
  once in one let-type block.
AND and OR are now implemented in terms of IFs.
Improved error reporting + bug fix.

bug fix:

- there was an error in the parser that
  was keeping it from recognising an empty formal parameter list.
NIL can now be used as an actual parameter.
Improved error messages.