missing/empty files

[Dan Eble]

I have a couple of related suggestions.  These would be minor conveniences—so 
minor that I don’t care enough at the moment to implement them myself.

let convert-ly remain silent about files which contain only whitespace (or 
which are empty) rather than issuing an error that there is no \version 
statement

add a variant of \include which does nothing if the file does not exist 
(eliminating one reason to have empty files in the first place)
— 
Dan