Merge pull request #71 from khalifenizar/master

catch `fs.statSync()` error in `loadExercise()`
move `util/makews.js` to new `bin/` directory

Because of the existence of `util.js`, having `makews.js` in `util/` makes it awkward for tab completion and is confusing.
add `--force` arg to overwrite with `makews.js`
generate working exercises with `makews.js`

Use `workshopper-exercise` for `exercise.js` export.
update bundled example exercises

Working examples generated by `makews.js`.