Simplify the grammar of ParamBlock.

Remove the attribute list header from the ParamBlock grammar, which
wasn't needed, even though the specification lists it. Also,
allow the use of spaces and newlines, not just newlines as separators
for the grammar parts.
Allow spaces, as well as newlines, as the separator for ScriptParameter.
Allow spaces between parts of Parallel and SequenceStatement.
Attributes can be separated by spaces in AttributeList.
Add tests for ParallelStatement, SequenceStatement and ParamBlock.