Selected maps

The plugin produces a large number of mappings.  I, and I suspect many users, only actually use a small subset of the mappings.  Having all those extra mappings lying around seems unnecessary and they may conflict or overwrite other mappings the user has.  For new users, it makes sense to create the mappings by default, but it would be nice to have an option so that the user might create only the mappings that he or she needs.  This pull request is my attempt to add a new option that prevents the creation of mappings except if the user has explicitly defined a mapping.