Add const qualifier to equals

libwccl/values/bool.h

@@ -23,7 +23,7 @@ public:
 		val_ = v;
 	}
 
-	bool equals(const Bool& other) {
+	bool equals(const Bool& other) const {
 		return val_ == other.val_;
 	}
 

libwccl/values/positionref.h

@@ -54,7 +54,7 @@ public:
 				(base_->get_value() == Position::End && offset_ > 0);
 	}
 
-	bool equals(const PositionRef& other) {
+	bool equals(const PositionRef& other) const {
 		return points_nowhere() ? other.points_nowhere()
 			: offset_ == other.offset_ && base_->equals(*other.base_);
 	}