To-Do List
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 * support comparison of tumbler to span
 * support comparison of span to tumbler
 * provide a tumbler-to-int converter that raises an exception if not possible __int__
 * how to reconcile addition with concatenation
 * study os.path and create equivalents for tumblers
 * AddrTumbler attributes: .node  .account  .document  .atom  .atomtype  .atomsuffix
 * consider: summation of spans creates a spec/vspec/sporgl/???
