Silence logging in venn.diagram

[stefaneng]

The default behavior for venn.diagram is to write a log to file. There is an argument disable.logging which prevents logging to file and prints to stdout but no option to silence logging output. It would be nice to have a third option which is no logging output.

Idea solution: Default is silent with no logging, except warning or errors as standard. Opting in to logging is the nicer default for most users and is the standard in plotting packages.

[pboutros]

I like the idea of overloading the disable.logging argument to allow silent, but I'd prefer to not change the default