anchor.diff:  * <<start,getting started>>
   * <<testing,testing>>
   * <<types,types>>
  -* <<ctors,construction>>
  +* <<ctors,constructors>>
   * <<axioms,axioms>>
   * <<keys,Keys, keychains, keylinks, dogtags>>
   * <<kinds,kinds>>
  
positive.code: 
  These are represented in migae as `entity-map` and `keychain`, respectively.
  
  == [[ctors]]construction
  
  We have three ways to construct PersistentEntityMap objects:
  
  
negative.code: ----
  etc.  More to come.
  
  
  == [[keys]] keys, keychains, keylinks, and dogtags
  
  A keylink is a namespaced keyword, e.g. `:Foo/Bar`.  A vector of
  keylinks is a keychain, which corresponds to a datastore Key, which
  