Release 0.12.0

Author: andrewrk

doc/langref.html.in

@@ -314,6 +314,7 @@
           <a href="https://ziglang.org/documentation/0.9.1/">0.9.1</a> |
           <a href="https://ziglang.org/documentation/0.10.1/">0.10.1</a> |
           <a href="https://ziglang.org/documentation/0.11.0/">0.11.0</a> |
+          <a href="https://ziglang.org/documentation/0.12.0/">0.12.0</a> |
           master
         </nav>
         <nav aria-labelledby="table-of-contents">