Expose enrg_md_steps option in mrdna and enrgmd scripts and in mrdna.simulate.multiresolution_simulation(); thanks to Elija Feigl for the suggestion

Added fill_sequence parameter to SegmentModel.set_sequence and to the mrdna and enrgmd scripts, with default value 'T', since that is most common for origami. Thanks to Elija Feigl for recommending the change.

Added support for reading in orientation; added enrgmd script for output enrgmd files without running simulations