single frame support in dcd
Added support for frames in openmm_positions and openmm_boxes
Removed openmm_*_all functions
Intermediate checkin of trajectory changes for join() with discard_overlapping_frames
Merge remote-tracking branch 'upstream/master' into single_frame
Added docstrings for discard_overlapping_frames
reworked filenames loading per RMG
Check all filetypes in trajectory.load()
Fixed tests, added more tests of load()
Moved all [filenames] logic to load() rather than load_x()
Merge pull request #17 from kyleabeauchamp/single_frame

[WIP] single frame support in dcd