Put definitions for constants for Nowhere, End, Begin.

My relative position tests wouldn't compile in GCC where I used Position::Nowhere for comparison. Apparently according to standard TC1, section 9.4.2, paragraph 4, if you want to use integral static const in a program, you still have to define it even if there's initializer in the declaration.

libwccl/values/position.cpp

@@ -6,6 +6,10 @@ namespace Wccl {
 
 const char* Position::type_name = "Position";
 
+const int Position::Nowhere;
+const int Position::End;
+const int Position::Begin;
+
 std::string Position::to_raw_string() const
 {
 	switch (val_) {