Implemented apply()

Author: hosseinmoein

docs/HTML/DataFrame.html

@@ -528,6 +528,10 @@ <H2 ID="2"><font color="blue">API Reference with code samples <font size="+4">&#
       <td title="These are other functionalities of DataFrame" style="text-align:center;background-color:DarkGrey;color:DarkBlue">Miscellaneous</td>
     </tr>
 
+    <tr class="item" onmouseover="this.style.backgroundColor='#ffff66';" onmouseout="this.style.backgroundColor='#d4e3e5';">
+      <td title="Applies function to the given column(s)"><a href="https://htmlpreview.github.io/?https://github.com/hosseinmoein/DataFrame/blob/master/docs/HTML/apply.html">apply</a>( 3 )</td>
+    </tr>
+
     <tr class="item" onmouseover="this.style.backgroundColor='#ffff66';" onmouseout="this.style.backgroundColor='#d4e3e5';">
       <td title="Generates categorical column from one-hot indicators"><a href="https://htmlpreview.github.io/?https://github.com/hosseinmoein/DataFrame/blob/master/docs/HTML/load_indicators.html">from_indicators()<BR>load_indicators()</a></td>
     </tr>