[Feature] ignore comments inside article

[miurahr]

Is your feature request related to a problem? Please describe.
DSL specification defines comment {{ commnet }} it should be ignored.

Describe the solution you'd like
Update JavaCC syntax definition to accept comment

Describe alternatives you've considered
To allow client to handle comment contents, dsl4j don't ignore but call visitor with comment content.

Additional context
Visitor interface will be extend, but we can define default method which just ignore it.