LGTM.com-inspired changes:

- Fix: Ensure all apostrophes are escaped for `toXml` utility
- Fix: Avoid error if `URL` is not defined
- Fix (jPicker): Precision argument had not been passed in previously
- Fix (Star extension): Minor: Avoid erring if `inradius` is `NaN`
- Refactoring: Avoid passing unused arguments, setting unused variables,
  and making unnecessary checks; avoid useless call to `createSVGMatrix`
- Linting (LGTM): Add `lgtm.yml` file (still some remaining items flagged
  but hoping for in-code flagging)
- Docs: Contributing file

screencasts/svgopen2010/script.js

@@ -272,7 +272,7 @@ SlideShow.prototype = {
 };
 
 // Initialize
-const slideshow = new SlideShow(query('.slide')); // eslint-disable-line no-unused-vars
+/* const slideshow = */ new SlideShow(query('.slide')); // eslint-disable-line no-new
 
 document.querySelector('#toggle-counter').addEventListener('click', toggleCounter, false);
 document.querySelector('#toggle-size').addEventListener('click', toggleSize, false);