Rover

> **NOTE:** ROVER should be installed from PyPI: https://pypi.org/project/rover/, usually via `pip`. Do not install ROVER from these downloads.

* Remove Python 2 support, ROVER is now only supported on Python 3.8 or later
* Remove leap second file handling, now unnecessary
* Convert setup.py to pyproject.toml for modern packaging support
* Fix robot tests and convert nose tests to pytest
* Convert to new EarthScope branding and theme on documentation site

* Change documentation links from IRIS to EarthScope

> **NOTE:** ROVER should be installed from PyPI: https://pypi.org/project/rover/, usually via `pip`. Do not install ROVER from these downloads.

* Adapt ROVER to use the DMC's new fdsnws-availablity service
* Fix printing of error message on download failures

> **NOTE:** ROVER should be installed from PyPI: https://pypi.org/project/rover/, usually via `pip`. Do not install ROVER from these downloads.

* Add change log to documentation
* Fix `list-retrieve` printing of single instance/sample cases.

* Optionally install `mseedindex` as a simply PyPI dependency, independent of ROVER.