add support for HLSL/FX

Add support for DirectX HLSL / FX files. The FX files are
just HLSL files with some additional syntax to set
render-states and define multiple shader stages in one file.

Samples are either written by me, or taken from Chromium.

lib/linguist/languages.yml

@@ -1323,6 +1323,16 @@ HCL:
   ace_mode: ruby
   tm_scope: source.ruby
 
+HLSL:
+  type: programming
+  extensions:
+    - .fx
+    - .fxh
+    - .hlsl
+    - .hlsli
+  ace_mode: text
+  tm_scope: none
+
 HTML:
   type: markup
   tm_scope: text.html.basic