fix fermi_hubbard/publication_test by updating datadryad download URLs since they appear to have changed (#166)
fix fermi_hubbard/publication_test by updating datadryad download URLs since they appear to have changed (#166)

* add a library containing mcpe calculation utilities, DependencyLists and QubitMapping data structures, and implement the swap update algorithm

* remove iswap factory and replace swap factory with sqrt-iswap decomposition

* fix typo

* replace _adjacent_qubits() with GridQubit.neighbors() and remove SwapUpdateTransformer

* replace assert's with ValueError's, update manhattan distance TODO, and add test coverage for previously untested public functions

* refactor swap updater tests

* update datadryad download URLs since they appear to have changed
quantumlib/unitary,quantumlib/ReCirq,quantumlib/unitary,quantumlib/ReCirq