Add support for the GDScript language

References:
* https://github.com/okamstudio/godot/wiki/gdscript
* http://www.godotengine.org/

Some projects using it:
* https://github.com/okamstudio/godot
* https://github.com/Qwertie-/Godot-games

My motivation for adding it: To disambiguate these .gd
files from GAP .gd files.

samples/GDScript/example.gd

@@ -0,0 +1,57 @@
+# Taken from https://github.com/okamstudio/godot/wiki/gdscript
+# a file is a class!
+
+# inheritance
+
+extends BaseClass
+
+# member variables
+
+var a = 5 
+var s = "Hello"
+var arr = [1, 2, 3]
+var dict = {"key":"value", 2:3}
+
+# constants
+
+const answer = 42
+const thename = "Charly"
+
+# built-in vector types
+
+var v2 = Vector2(1, 2)
+var v3 = Vector3(1, 2, 3)
+
+# function
+
+func some_function(param1, param2):
+    var local_var = 5
+
+    if param1 < local_var:
+        print(param1)
+    elif param2 > 5:
+        print(param2)
+    else:
+        print("fail!")
+
+    for i in range(20):
+        print(i)
+
+    while(param2 != 0):
+        param2 -= 1
+
+    var local_var2 = param1+3
+    return local_var2
+
+
+# subclass
+
+class Something:
+    var a = 10
+
+# constructor
+
+func _init():
+    print("constructed!")
+    var lv = Something.new()
+    print(lv.a)