Add 'GLOBAL' keyword #122

Also provides functionality that makes things like overriding the built in
'print' possible. See #67

include/chaiscript/language/chaiscript_common.hpp

@@ -38,7 +38,7 @@ namespace chaiscript
                 Comparison, Addition, Subtraction, Multiplication, Division, Modulus, Array_Call, Dot_Access, Quoted_String, Single_Quoted_String,
                 Lambda, Block, Def, While, If, For, Inline_Array, Inline_Map, Return, File, Prefix, Break, Continue, Map_Pair, Value_Range,
                 Inline_Range, Annotation, Try, Catch, Finally, Method, Attr_Decl, Shift, Equality, Bitwise_And, Bitwise_Xor, Bitwise_Or, 
-                Logical_And, Logical_Or, Reference, Switch, Case, Default, Ternary_Cond, Noop, Class, Binary, Arg
+                Logical_And, Logical_Or, Reference, Switch, Case, Default, Ternary_Cond, Noop, Class, Binary, Arg, Global_Decl
     };
   };