adding pytables to travis configuration
Initial commit illustrating io with pytables
Fix path in unit tests
pep8 fixes
fixing imports
adding valid method
making open a classmethod
adding documentation
moving files into io
deleted files
adding bonds to abc/file particle container
adding missing bond.py needed for previous commit
remove duplicatd code block
removing returns
fixing spelling
Improving the iterators by making use of pytables (iterrows)

For iterating over 1000 particles this improved the time from around ~36s
to ~0.37s
fixing default argument for data
changing exceptions to ValueError
Merge branch 'master' into feature-io-particles
fix flake8 violation