- added three features that together allow us to solve new types of problems. ex. you want to get from one axle to another and have the biggest gear ratio.
  1. no longer required to specify a ratio in an objective
  2. added a parameter to the solve-gear-ratio (two-gears-on-one-axle-allowed?) that allows us to put more than one gear on an axle.
  3. added a procedure that finds the solutions with the best ratios.
- gear-ratios.rkt: commented out some badly matched gear combinations