Parity with Freebie

I'm stuck on EE 1.6.x for a site I'm working on, but wanted to do a lot of the thing that Freebie handles for 2.0, so I've added them in to NSM Safe Segments. You're welcome to merge them in to the main version if you like.

Key improvements:  
- it can now break on segments after a keyword  
- it can now automatically replace the default category keyword handling  
- it now parses break after segments into sets of variables, so you can use multiple break words in the same URL (in a somewhat limited way)