Run tests with Karma test runner

Closes gh-566.

test/bootstrap.js

@@ -0,0 +1,12 @@
+/*jshint browser:true */
+
+var root = document.createElement( "div" );
+root.innerHTML = [
+  "<div id='impress'>",
+  "  <div class='step' data-x='-1000' data-y='0'>First slide</div>",
+  "  <div class='step' data-x='-800' data-y='0'>Second slide</div>",
+  "  <div class='step' data-x='-600' data-y='0'>Third slide</div>",
+  "  <div class='step' data-x='-400' data-y='0'>Fourth slide</div>",
+  "</div>"
+].join( "" );
+document.body.appendChild( root );