Merge tag 'v3.40.0' into develop

Updated code to fit newer Python releases (i.e. using `collections.abc` instead of `collections`). Fixes: #186 v3.40.0

# gpg: Signature made Mon May 27 17:03:43 2019 CEST
# gpg:                using RSA key 149325FD15904E9C4EB89E95E81444E9CE1F695D
# gpg: Good signature from "Rick van Hattem <wolph@wol.ph>" [ultimate]
# gpg:                 aka "[jpeg image of size 9662]" [ultimate]

Author: wolph