DataDescriptor.py[...] -> DataDescriptor[...]

Issue: this promotes python types as the default itemaccess type
Benefit: .py was confusing because it looked like a file extension
dd.py[...] -> dd[...] for compute(Projection, DD)
Add google analytics to docs
add pytables compute draft
small edits to pytables
numpy: fall back on pandas for by, join, ...
try to import pytables
fix pip install datashape command
pytables: compute column
add pytables testing file
add pytables to travis testing
Merge pull request #426 from aterrel/google-analytics

Add google analytics to docs
expr: selection doesn't fail on non-rowwise child

Effect is that nested selections or really any selection of a non-rowwise
is still acceptable.

Thanks @talumbau for reporting
expr: rowwise docstring
Merge pull request #445 from mrocklin/selection-path-check

expr: selection doesn't fail on non-rowwise child
minor edits to docs reflecting recent changes
doc: index header looks more like README
doc: start api documentation
doc: docstrings adhere to numpydoc
add numpydoc to conf.py