lone commas are allowed in array initializers
change spec to allow full Types in type arguments (instead of just identifiers)
and change implementation and AST to match

correctly (?) implement parsing of type arguments in the presence of multiple consecutive '>' symbols:  a Java implementation at
http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7-b147/com/sun/tools/javac/parser/JavacParser.java#JavacParser.typeArguments%28boolean%29
does this by reinterpreting tokens beginning with `>` during hierarchical parsing, if necessary, chopping a piece off and pushing back a shortened token.  This implementation basically does it the same way

introduce convenience combinators to reduce noise