Add signal style flag for drawing on the opposite side

docs/newgrf-additions-nml.html

@@ -512,6 +512,11 @@ item (FEAT_GLOBALVARS) {
 			The value is clamped to be less than or equal to the value set in the <span class="code">extra_aspects</span> property.
 		</td>
 	</tr>
+	<tr><td>style_opposite_side</td><td>0 or 1</td>
+		<td>
+			Set whether signals should be drawn on the opposite side of the track for the most recently defined style (defined using the <span class="code">define_style</span> property).
+		</td>
+	</tr>
 	<tr><td>no_default_style</td><td>0 or 1</td>
 		<td>
 			When enabled, custom signal graphics from this GRF are only used for custom signal styles, not the default style