Fix bug in _correlation_me_2op_2t

Fix _correlation_me_2op_2t to calculate <A(t)B(t+tau)> when
reverse=True, and <A(t+tau)B(t)> otherwise.
Merge pull request #27 from swhalen/correlation-fix-1

Fix bug in _correlation_me_2op_2t
experimentally added support for rhs_with_state in list-function mesolve
added 1d versions of expect_rho_vec
support for rhs with state in list function formats
minor python3 compatibility fix
WIP: experimental support for rhs_with_state python function callbacks in mcsolve
ADDED: function to reshape sparse matricies

sp_reshape()