Merge pull request #350 from mrocklin/imports

Imports
python: support By(t, t, t.reduction())

Previously we expected the grouper to be a projection.  Now we allow it to be
any rowfuncable
specify sqlalchemy float types
hdf5: tiny test showing varlen strings through h5py
CSV/SQL._extend([]) works
server: __init__.py
update travis.ymal and conda yaml to include toolz and cytoolz as runtime dependencies of blaze
Merge pull request #360 from quasiben/feature/conda_deps_update

Update runtime dependencies of blaze
sql: choose given schema if mismatch exists
Merge pull request #359 from mrocklin/small-fixes-2

Small fixes
Merge pull request #356 from mrocklin/sql-types

specify sqlalchemy float types
Merge pull request #354 from mrocklin/by-of-tablesymbol

python: support By(t, t, t.reduction())
hdf5: variable length string support via Python
add hdf5 to root imports
hdf5: discovery support strings
hdf5: variable length strings via python layer
import unicode from compatibility
discover nd.array
hdf5: use natural chunk size, __iter__ bypasses coerce
core doesn't enforce dtype in dynd if dshapes same