Support of the .vh file extension for SystemVerilog

lib/linguist/languages.yml

@@ -1660,6 +1660,7 @@ SystemVerilog:
   primary_extension: .sv
   extensions:
   - .svh
+  - .vh
 
 TOML:
   type: data

samples/SystemVerilog/util.vh

@@ -0,0 +1,8 @@
+function integer log2;
+  input integer x;
+  begin
+    x = x-1;
+    for (log2 = 0; x > 0; log2 = log2 + 1)
+      x = x >> 1;
+  end
+endfunction