Road stops: Add inferred one way road state to var 50/roadstop_misc_info

docs/newgrf-roadstops.html

@@ -309,6 +309,14 @@
 		2 - East-bound only<br />
 		3 - No entry
 	</td></tr>
+	<tr><td>2 - 3</td><td>
+		Inferred one-way road information, from examining the road layout:<br />
+		0 - Two-way traffic<br />
+		1 - West-bound only<br />
+		2 - East-bound only<br />
+		3 - No entry<br />
+		This requires <font face="monospace">road_stops</font>, version 8.
+	</td></tr>
 	</table>
 	<br />
 	The remaining bits are reserved for future use and should be masked.