templatekw: add default implementation of _hybrid.gen This is convenient for new template keyword, which doesn't need to support the legacy list hack (provided by _showlist()), but still wants to have a string representation.

parser: preserve order of keyword arguments This helps building dict(key1=value1, ...) in deterministic way.

parser: extend buildargsdict() to support arbitrary number of **kwargs Prepares for adding dict(key1=value1, ...) template function. More tests will be added later.