Experimental kerf implementation, not yet working
Massive refactor, and switching to using Vectors

 - code reorganization for clarity
 - tuple is now the owner of all move_by etc
 - vectors allow very clean math for moves
 - kerfing is almost there - just need to fix lengths
   of the tabs
Experimental kerf implementation, not yet working
minor tweak
Move ruby to 2.1.3 since I want to start using new syntax.
Another iteration on kerf, mostly working, just need to remove overlapping lines
Major fucking kerfing work, but it still fails :(

Maybe need to refactor the entire thing to make it work....
Lots of good changes, but kerf still not fully working.
Next: moving to proper geometry lib
Kerning is working (I think!)
Merge pull request #2 from kigster/kerf

Adding Kerf implementation – it's a bit ugly, but it goddamn works :)