[Petal] Modifiers and variables

[Jean-Michel Hiver]

>> I see. Well, I wouldn't adding a base class (i.e. Petal::Plugin) 
>> which would be the recommended method to implement new modifiers, and 
>> then cabling existing modifiers onto Petal::Plugin.
>
> I say, what a brilliant idea! :-) 

Which takes us to the problem of the syntax. We need to come up with a 
sort of grammar for the parser in this base class. Any ideas?