Breeds updates; new utilities; @asSet defaults return array of agentset's type.
- AgentSet:
  - set.exclude(breeds): return set without given breeds
  - asSet: experimental! set.asSet(a) returns a as same type as set.
    Before returned ABM.AgentSet type.
    Ex: patches.asSet(a) returns a as patches.
  - histOfProp: returns a histogram of the property
  - show/hide: added as.show/as.hide method, applies to all of the agentset.
  - histOfProps(prop,bin) added for easy histogram of agentset properties.
- AgentSets:
  - remove breed(breedName), no longer needed
- Model:
  - removed model.stopped() .. just use anim.stopped
  - removed setCachePatchRects; use @patches.cacheRect radius, meToo
  - reset(restart): add restart argument .. if true restart model after resetting.
- models/:
  - Experiment with new <agentset>.asSet(array)
  - Name change: nldroplets.html -> droplets.html
  - Droplets: move patch elevation processing to setup (for reset)
  - Droplets: add slope/aspect; useAspect flag to choose between elev & aspect