add margin to dl, fixes #43

sass/_theme_rst.sass

@@ -171,6 +171,7 @@
   // This makes me terribly unhappy and makes this code very nesty. Unfortunately I've seen hand-written docs
   // that output similar, but not quite the same nesting so this is really the best we can do.
   dl
+    margin-bottom: $base-line-height
     // This would be the equivilant of a .. class::
     dt
       display: inline-block