v1.0.6

• add baseref for nastruct #1255
• add view for trajectory #1253, #1250
• add symmrmsd #1245
• add autoimage, superpose, ... to pytraj.TrajectoryIterator
• add freq to NH_order_paramters method
• add velocityautocorr #1228
• add rotdif #1225
• add writing force and velocity #1223
• fix alignment for two structures with different topology #1249