Changed:
Structure definition syntax changes:
* The VAR: variable reference has been replaced by EVAL: which allows you to use any expression, even involving other variables. The result of the expression is used as the value (e.g. loop length).
* The "always ...?" syntax for defining fatal asserts has been changed to "assert ..."
* The "expect ..." syntax for non-fatal asserts has been introduced.
Parser changes:
* The Structure tuples yielded by parse now include a parameter "unexpected" that will be None if no expects are defined, True if any expects are False, or False if all expects are True.
* It is now possible to pass pre-defined variables to parse.
