remove few TODOs

parser.cpp

@@ -5,6 +5,17 @@ namespace usql {
 
 // TOOD handle premature eof
 
+	std::string column_type_name(const ColumnType type) {
+		if (type == ColumnType::integer_type)	return "integer_type";
+		if (type == ColumnType::float_type)		return "float_type";
+		if (type == ColumnType::varchar_type)	return "varchar_type";
+		if (type == ColumnType::date_type)		return "date_type";
+		if (type == ColumnType::bool_type)		return "bool_type";
+
+		throw Exception("invalid column type: " + (int)type);	
+	};
+
+
     Parser::Parser() {
 	    m_lexer = Lexer{};
     }
@@ -529,4 +540,3 @@ namespace usql {
     }
 
 }	// namespace
-