fix: Reduce number of created inotify instances #275 (#1099)

* re: #275 reduced number of created inotify instances - first draft

* re: #275 fixed race conditions from inotify

* re: #275 fixed test_inotify_c.py

* re: #275 fixed test_inotify_buffer.py

* re: #275 renamed test_inotify_buffer.py to test_inotify_watch.py

* re: #275 ignore error when removing a watch that doesn't exist anymore

* re: #275 fixed some docstrings

* re: #275 renamed InotifyBuffer to InotifyMoveEventGrouper

* re: #275 renamed InotifyWatch to InotifyWatchGroup

* re: #275 added clarifying comments

* re: #275 added test case for independence of InotifyWatchGroups

* re: #275 renamed test_inotify_watch_grouper.py to test_inotify_watch_group.py

* re: #275 removed superfluous todos

* re: #275 fixed too early import in test

* re: #275 fixed python 3.9 compatibility

* re: #275 fixed python 3.9 compatibility

* re: #275 fixed linter issues

Author: JoachimCoenen