np.mean fails for list of sparse matrices. use np.sum + division instead
updated docstrings related to average_states and average_expect
Merge pull request #204 from jrjohansson/fix-mcsolve-average_state

Fix mcsolve average state
fix bug in mcsolve with num_cpus=1 (expectation value data must be copied or it will be overwritten by simulation of the next trajectory)
Merge pull request #205 from jrjohansson/fix-mcsolve-serial-bug

fix bug in mcsolve with num_cpus=1