message: Improve TLS support
  Fix issue found when trying to run keras predict in separate thread(s).
diff: import logging
  import os
  import platform
  -import sys
  import threading
  import pkg_resources
  from plaidml._ffi import ffi
  -logger = logging.getLogger(__name__)
  -_TLS = threading.local()
  -_TLS.err = ffi.new('plaidml_error*')
  +class ThreadLocalState(threading.local):
  +
  + def __init__(self):
  + self.err = ffi.new('plaidml_error*')
  +
  +logger = logging.getLogger(__name__)
  +_TLS = ThreadLocalState()
  _LIBNAME = 'plaidml'
  if platform.system() == 'Windows':
  