The parser must accept sentences whose role has a comma at the end

[plevyieml]

IEML Grammar requires that the roles in a sentence end with a comma, except for the penultimate role. The last role ends with a period. But a comma at the penultimate part does not create ambiguity.

[ogrergo]

The following code snippet must be accepted by the parser :

@word "a.". 
@word "b.".
@node en:node1 (0 #"a.", 1 #"b.",).

At the moment, the parser will complain that there is an extra , after #"b.". This should not cause any issue with the grammar, and it causes unnecessary pain for the user.