Update change log
Update change log

Mention:
* single-mpi
* remove --mode required option on flux
* randomize velocities
* HPMC cluster updater
* patch implicit
* patch.user_union performance improvments
* MPCD
* TBB
* metadata fixes
* seg fault in patch.integrate.*_union
* pybind 2.2

joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue