Add F# and GLSL samples. Add Forth and GLSL extension .fs.

Add heuristic to disambiguate between F#, Forth, and GLSL.

lib/linguist/heuristics.rb

@@ -39,6 +39,9 @@ module Linguist
         if languages.all? { |l| ["FORTRAN", "Forth"].include?(l) }
           result = disambiguate_f(data)
         end
+        if languages.all? { |l| ["F#", "Forth", "GLSL"].include?(l) }
+          result = disambiguate_fs(data)
+        end
         return result
       end
     end
@@ -151,6 +154,18 @@ module Linguist
       matches
     end
 
+    def self.disambiguate_fs(data)
+      matches = []
+      if /^(: |new-device)/.match(data)
+        matches << Language["Forth"]
+      elsif /^(#light|import|let|module|namespace|open|type)/.match(data)
+        matches << Language["F#"]
+      elsif /^(#include|#pragma|precision|uniform|varying|void)/.match(data)
+        matches << Language["GLSL"]
+      end
+      matches
+    end
+
     def self.active?
       !!ACTIVE
     end