hdf5: tiny test showing varlen strings through h5py
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
blen defaults to 1024 is arr.chunks not set
set default coercion block to size 1024

The power-of-two size should integrate well with HDF5 auto chunking
hdf5: select multiple fields
hdf5: increase number of chunks to pull out for each _chunk
hdf5: multiple fields for dynd

Also into(tuple, nd.array)
simplify HDF5 interface, remove mode
add comment about nd.array(..., type=) performance
Merge pull request #358 from mrocklin/hdf5-varlen-strings

HDF5 variable length strings