retire the use of `gulp` in this repo

There are four gulpfile.js files in this repo:

[x] gulp-and-css-handling/gulpfile.js [src] and its parent folder can be completely removed 🔥
[x] jquery-audio5/gulpfile.js can be replaced by concat [npm]
[x] svg-and-object-element/gulpfile.js can be replaced by the ImageMagick convert CLI in an npm script
[x] tiffany-rayside-svg-verlet/gulpfile.js appears to used for a one-time conversion (?) and can be removed

BryanWilhite / nodejs