Mention supported operating systems. Refs #548

…f baked args

Add python 3.9

Let Command know about baked call args when wrapping the module

…tion docs

Rip out test running code in sh.py, and attempts in test.py to set up coverage. Instead, let Actions script handle coverage and env var matrix.

Switch from Travis to GitHub Actions

…lable

CWD may be /tmp on some systems

fix flaky test

Fix #597.
I decided to not add an additional import for `pathlib.Path` and instead check if the object passed is "path-like" according to [PEP-519](https://www.python.org/dev/peps/pep-0519/).

This is an exception to the rule and is needed to provide backwards compatibility.

While Python 3.5 introduced pathlib, __fspath__ wasn't introduced until Python 3.6

This fixes a deadlock by only locking the assignment of self.exit_code

Accept pathlib.Path objects for stdout/stderr

Allow done callback to access RunningCommand

Make sh.which() an internal function