jQuery: JSDoc completeness within reach

well nearly
jQuery: tests now cast to svgjs.LinkedHTMLElement

This could be made implicit by extending the JQuery interface with:
get(index: number): svgjs.LinkedHTMLElement;

Looking at the library it didn't seem sensible to create a dependency on
jQuery even though the tests have one.
jQuery: Put back in what I accidentally removed
Merge pull request #1839 from johnnyreilly/master

jQuery: JSDoc completeness within reach