Executor: Programmer friendly subprocess wrapper

The `executor` package is a simple wrapper for Python's `subprocess` module, designed to simplify handling external commands on UNIX systems. It provides an object-oriented interface with proper argument escaping and error checking. Features include support for local commands, remote commands over SSH, execution within chroots, and concurrent command execution through command pools. The library's latest version is 23.2, released in November 2020, with an irregular release cadence.