Include skipto.js to the examples/js folder for wai-aria-practices compatibility

[evmiguel]

Currently, the wai-aria-practices script, which formats the examples for APG, depends on the files in the examples/js folder. The script copies over the *.js files in that folder to make the Jekyll site.

What's currently missing is the skipto.js file, which is being referenced in this portion of the code , which was previously jumpto.js. As a result, the build script fails.

skipto.js was added to a location in the wai-aria-practices repo which can be overwritten (in this PR). Would it be possible to copy over skipto.js to this repo's examples/js folder to fix the build script?

cc: @jongund

[richnoah]

@evmiguel clearance given by Task Force to move skipto.js to this repo.