Check for energy-dependent multiplicity in ACE file.
Merge pull request #296 from paulromano/multiplicity

Check for energy-dependent multiplicity in ACE file

All tests pass; merging and closing.
Fix distance-to-surface calculationg for general plane surface.
Change quick install instructions to be more explicit about checking out branch
master.
Have update_results.py run OpenMC twice when generating results for
test_source_file. Closes #288 on github.
Merge pull request #299 from paulromano/plane-distance-fix

Fix distance-to-surface calculation for general plane surface