docs: insert spaces between classes and methods in docs (#133)

Author: busunkim96

docs/_static/custom.css

@@ -1,9 +1,20 @@
 div#python2-eol {
 border-color: red;
 border-width: medium;
-} 
+}
 
 /* Ensure minimum width for 'Parameters' / 'Returns' column */
 dl.field-list > dt {
  min-width: 100px
 }
+
+/* Insert space between methods for readability */
+dl.method {
+padding-top: 10px;
+padding-bottom: 10px
+}
+
+/* Insert empty space between classes */
+dl.class {
+padding-bottom: 50px
+}