Implement breed.setBreed(agent) for patches/agents/links.
Main innovation: allow patch breeds.
- All: Use "unless" rather than "if not" if reasonable.
- Util:
  - Convert binarySearch to underscore's sortedIndex w/ some additions
  - Add indexOf based on sortedIndex
  - Performance test of fixed() vs Number(n.toFixed(p)); ours is much faster
  - Performance test of nOf vs sort/shuffle; ours much faster
  - nOf: round n, insure <= array.length, remove error
  - add @propFcn, @identity
- AgentSet
  - ctor: add breeds array, init to []
- AgentSets:
  - Patches: add populate method to fill in grid
  - Patches: ctor populates only when not a subarray/breed (Allows patchBreeds)
  - Add class/prototype variable defaults for all instance variables; update docs
- DataSet:
  - Add option to eliminate NaNs from slopeAndAspect's aspect.
- Models:
  - Convert to new Patches/populate model
  - Convert from changeBreed (agents only) to agentset.toBreed(a) (general)
  - breeds: move from ABM.patchBreeds to @patches.breeds etc for agents/links
  - debug() returns model for chaining