message: Added docs for SlopeVisitor
diff: @@ -726,6 +726,10 @@ table.hovertable td {
  <td title="Visitor adopter for rolling">struct <a href="https://htmlpreview.github.io/?https://github.com/hosseinmoein/DataFrame/blob/master/docs/HTML/SimpleRollAdopter.html">SimpleRollAdopter</a>{ }</td>
  </tr>
  + <tr class="item" onmouseover="this.style.backgroundColor='#ffff66';" onmouseout="this.style.backgroundColor='#d4e3e5';">
  + <td title="Calculates slope of the diff">struct <a href="https://htmlpreview.github.io/?https://github.com/hosseinmoein/DataFrame/blob/master/docs/HTML/SlopeVisitor.html">SlopeVisitor</a>{ }</td>
  + </tr>
  +
  <tr class="item" onmouseover="this.style.backgroundColor='#ffff66';" onmouseout="this.style.backgroundColor='#d4e3e5';">
  <td title="Calculates simple linear regression">struct <a href="https://htmlpreview.github.io/?https://github.com/hosseinmoein/DataFrame/blob/master/docs/HTML/SLRegressionVisitor.html">SLRegressionVisitor</a>{ }</td>
  </tr>
  