docs(ngShowHide): improve consistency in ngShowHide documentation

add backticks around directive names to improve documentation consistency

Author: maip

src/ng/directive/ngShowHide.js

@@ -6,8 +6,8 @@
  *
  * @description
  * The `ngShow` directive shows or hides the given HTML element based on the expression
- * provided to the ngShow attribute. The element is shown or hidden by removing or adding
- * the `ng-hide` CSS class onto the element. The `.ng-hide` CSS class is predefined
+ * provided to the `ngShow` attribute. The element is shown or hidden by removing or adding
+ * the `.ng-hide` CSS class onto the element. The `.ng-hide` CSS class is predefined
  * in AngularJS and sets the display style to none (using an !important flag).
  * For CSP mode please add `angular-csp.css` to your html file (see {@link ng.directive:ngCsp ngCsp}).
  *
@@ -19,13 +19,13 @@
  * <div ng-show="myValue" class="ng-hide"></div>
  * ```
  *
- * When the ngShow expression evaluates to a falsy value then the ng-hide CSS class is added to the class
- * attribute on the element causing it to become hidden. When truthy, the ng-hide CSS class is removed
+ * When the `ngShow` expression evaluates to a falsy value then the `.ng-hide` CSS class is added to the class
+ * attribute on the element causing it to become hidden. When truthy, the `.ng-hide` CSS class is removed
  * from the element causing the element not to appear hidden.
  *
  * ## Why is !important used?
  *
- * You may be wondering why !important is used for the .ng-hide CSS class. This is because the `.ng-hide` selector
+ * You may be wondering why !important is used for the `.ng-hide` CSS class. This is because the `.ng-hide` selector
  * can be easily overridden by heavier selectors. For example, something as simple
  * as changing the display style on a HTML list item would make hidden elements appear visible.
  * This also becomes a bigger issue when dealing with CSS frameworks.