Macros with formal arguments can have default text for those arguments.
Generalize struct member type
Unions through pform.
Handle packed unions properly during elaboration.

This also gets r-value use of packed unions correct.
More relaxed handling of types of packed struct members as l-values.
Handle some assertion syntax in the parser.

Implement some yacc rules for assertion syntax.

Add the -gassertions/-gno-assertions command-line flags to
enable or disable assertions.
Handle enumerations as packed struct/union members.

There were also some subtleties related to using enumerations
from typedefs and using them in multiple places. Fix various
bugs related to those issues.
Merge branch 'master' of git://github.com/steveicarus/iverilog