Tasklib

The latest `tasklib` release is now [available on Pypi](https://pypi.org/project/tasklib/2.5.1/).

The 2.4.3 bugfix release improves compatibility with Taskwarrior 2.6.0 by fixing the determination of tasks' waiting status.

This is a recommended upgrade.

This recommended release adds several compatibility improvements:
* Support for Taskwarrior 2.6
* Support for `tzlocal>=3.0`
* Official support for Python 3.9 in the test matrix

A long standing library bug was discovered (97) and subsequently fixed (101). This could cause problems when tasks were completed or deleted before using tasklib scripts that add tasks.

Notably, this release also increases the minimum supported version of TW to 2.4.0 (released in January 2015).