Merge pull request #228 in LCL/wolframclientforpython from release/B12_1_0 to master

* commit '7f32c354bf697d963121f00b64ccd800028b6c2f':
  removing unused vars for clarity
  Add test with big real and neg exponent.
  Negative exponent is dropped when deserializing big reals
  add test to ensure sslcontext is initialized correctly
  Warning should be displayed once and for all
  multithreading module does not exist
  remove useless pass
  increment version
  Update changelog
  aiohttp based classes now use certifi
  update ssl api

Author: crazyeng