0.2.0

Added

• A hint in the documentation about implementing AutoTransIter for references.
• TransPrioQueue, a transitive priority queue, and functions for creating such
  a queue from a TransIter, including documentation and a test.
• Examples illustrating the use of the library's iterators for shortest-path
  searches.

Changed

• Items referred to in documentation text are now actual references.
• A confusing piece of documentation regarding a blanket implementation was
  rewritten.
• The test tests::node_order_breadth_first was rewritten for better
  performance (but still takes significantly more time than any other test).