platform-agnostic external command execution library for Python

 command_runner's purpose is to run external commands from Python, just like
 subprocess on which it relies, while solving various problems a developer may
 face among:
 - Handling of all possible subprocess.popen / subprocess.check_output
   scenarios / Python versions in one handy function without encoding or
   timeout hassle
 - Allow stdout/stderr stream output to be redirected to callback functions /
   output queues / files so you get to handle output in your application while
   commands are running
 - Callback to optional stop check to stop execution from outside command_runner
 - Callback with optional process information to allow control of the process
   from outside command_runner
 - Callback when finished to ease thread usage
 - Optional process priority and io_priority settings
 - System agnostic functionality, the developer shouldn't carry the burden of
   Windows & Linux differences
 - Optional Windows UAC elevation module compatible with CPython, PyInstaller,
   and Nuitka
 - Optional Linux sudo elevation compatible with CPython, PyInstaller & Nuitka