renamed bmp images to png (only type supported)

added all images to widget documentation
fixed some spelling / formatting errors

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@2226 8e941d3f-bd1b-0410-a28a-d453659cc2b4

components/nvidia-widgets/doc/nvwidgets/uicontext.docheckbutton.html

@@ -63,6 +63,8 @@
 <h2>Function result</h2>
 <p>True if the check button state changed</p>
 <h2>Description</h2>
-<p>Check button behaves similarly as a toggle button used to display and edit a bool property.</p>
+<p>Check button behaves similarly as a toggle button used to display and edit a boolean property.</p>
+<img alt="" src="../images/checkbutton.png">
+
 </body>
 </html>