CLN: modernize compat + remove cruft
last range fixes
Fix thread imports for Python 3
add missing six import to io/stata
Remove wildcard import from test_merge and fixup
thread's get_ident only needed in 2.6
CLN: basestring --> six.string_types
CLN: Use py3compat's StringIO
CLN: Py2/3 compatible __builtin__
make _WINDOW_TYPES update 2/3 compatible
remove unnecessary imports from io/__init__
CLN/ENH: Refactor url methods to be Py2/3 compatible
CLN: Use py2/3 compatible pickle import
CLN: py2/3 compatible unichr
CLN: Py2/3: callable --> six.callable
import fixes to wrap it all together
fixup erroneous find/replace
Py2/3 StringIO usage