Merge pull request #521 from swails/master

Make unit cell vector components that are almost zero exactly zero.
Update README.md
Added pdb conect fix and test
Added docstring for test
Add fix and test for 1ncw
Give explicit error when models have different numbers of atoms.
Merge pull request #527 from kyleabeauchamp/fixconnect

[WIP] Fix bug in CONECT reader in pdb
Fix apt?
Merge pull request #529 from rmcgibbo/fix-apt

Fix apt?
Write REMARK header indicating MDTraj in output PDB files.
Merge pull request #531 from kyleabeauchamp/pdbremark

Write REMARK header indicating MDTraj in output PDB files.
Added fix and tests for loading gzipped PDB
Hopefully fixes PY3 issues
Merge pull request #533 from kyleabeauchamp/gzfix

Added fix and tests for loading gzipped PDB
Change example resSeq to 1-based indexing. Closes #534
Update rotation.py
put current version in errmsg
Merge pull request #537 from rmcgibbo/errmsg

Put current version in import error message.
Fix docstring for topology.select_atom_indices. closes #538
Merge branch 'master' of github.com:rmcgibbo/mdtraj