added save function to OrderParameter for convenience
added save function to OrderParameter for convenience

dwhswenson/openpathsampling,openpathsampling/openpathsampling,choderalab/openpathsampling,choderalab/openpathsampling,choderalab/openpathsampling,dwhswenson/openpathsampling,dwhswenson/openpathsampling,openpathsampling/openpathsampling,dwhswenson/openpathsampling,jhprinz/openpathsampling,openpathsampling/openpathsampling,jhprinz/openpathsampling,openpathsampling/openpathsampling,jhprinz/openpathsampling