* Feature: echo. Can capture `stdout` from the command line execution.
* Feature: log to file. Can write what you can see on the screen to file, including those "echoed" from child processes.
* UX: added sphinx and our document is now available on [readthedocs.org/matrixtest](https://matrixtest.readthedocs.io/en/latest/index.html)
* Compatibility: Relaxed Python version requirement