first draft of discovery function
string coercions
discover tuples
discover dict
integrative test
discover bools
discover datetimes with dateutil
discover complex, fix bool
discover supports numpy
add dateutil to requirements
dateutil -> python-dateutil
discover: use _strtypes
discover: unite function
discovery:  Infer option from overlapping tuples
check for None before dimension

also py3 fix
fix imports in discovery
discovery: handle null entries in Records
discover datashape of None->null
clean up discovery
lowest_common_dshape