Practice on creating ul lists in JavaScript
Given an ul:
<ul id="elem"></ul>
Given an array. Insert the elements of this array
at the end of ul so that each element is
in its own li.
Modify the previous task so that when you click on any of the inserted elements, the text of this element is displayed on the screen.
Modify the previous task so that clicking on a
li adds '!' to its end.
Modify the previous task so that pressing the
li again doesn't add a second '!'.
