docstring and type checking for create sim from snap
docstring and type checking for create sim from snap

* hoomd.Snapshot and gsd.hoomd.Snapshot are documented as arg types
* these snapshot types are checked explicitly and TypeError is raised if type is neither accepted snapshot

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