Log Message:
py-w3lib: updated to 1.19.0

1.19.0:
- Add a workaround for CPython segfault (https://bugs.python.org/issue32583)
  which affect w3lib.encoding functions. This is technically **backwards
  incompatible** because it changes the way non-decodable bytes are replaced
  (in some cases instead of two ``\ufffd`` chars you can get one).
  As a side effect, the fix speeds up decoding in Python 3.4+.
- Add 'encoding' parameter for w3lib.http.basic_auth_header.
- Fix pypy testing setup, add pypy3 to CI.