A few general additions and small changes

* Added `.gitignore` with a couple sensible entries.
* Added `package.json` to handle npm dependencies (`npm install -d` wasn't working without this).
* A few minor editions and improvements to `README.md`.
* Enabled JS' *strict mode* in both JS files.
* All variable declarations *hoisted*.
* Better indentation.
* Removed extra trailing blank lines.
* Set `yargs` parameters by default; no need to pass them now.
* More compact expressions.
* Documented the new optional parameters, with their default values.