nat 1.8.5

The main feature of this release is improved support for nat+CMTK on Windows.

• teach voxdims.character to get voxel dimensions straight from image file on
  disk enhancement (#303)
• teach coord2ind to accept nat.templatebrains objects for imdims (#302)
• add simple smooth_neuron function (#300)
• fix bug reading amira surfaces when Color precedes Id (#305)
• cmtk.reformatx needs to use system2 (#301)
• Don't use shell features on Windows (#295)