Allow not mapping keys by default

I've been using this change for a while, and is time to propose upstreaming it.

It just adds a check on a variable to skip mapping stuff, since some people like it this way (e.g. me, since neocomplete already shows the menu). I set up the variable to 1 by default, since that doesn't break current users's setup, but I would set it to 0, so that would make future users that don't like their mappings to be touched less angry. :smile: 

Greetings.