KERML — Comment textual syntax defined differently to implementation

Example Vehicle Example/VehicleDefinitions.kerml does not parse if the grammar from the document is used.

Comment is defined in the document as

Comment =
  'comment' Identification
  (  'about'  Annotation ( ',' Annotation )*  )?
 REGULAR_COMMENT

and in the implementation as

Comment returns SysML::Comment :
	( 'comment' Identification?  ('about'  Annotation  ( ',' Annotation )* )?  )?
	REGULAR_COMMENT
;

Correct the Comment production

The Comment production from the specification, as shown in the issue description, is incorrect. It should be possible to have a comment that syntactically consists simply of a REGULAR_COMMENT token (e.g., of the form "/* ... */"), without the comment keyword. The production needs to be updated to allow this (as is the case in the production from the implementation also shown in the issue description).