Note's
* exports the mesh without modifiers or transformations applied
* supports UV's vertex colors
* no support for normals yet (missing from data api)
* registers an operator called EXPORT_OT_ply
* no file selector yet. can only fun from python currently
bpy.ops.EXPORT_OT_ply(filename="/tmp/test.ply")
* removed double lookups on the vertex dict, build face verts to write allong the way.
