some refactorings

usql/settings.cpp

@@ -19,7 +19,7 @@ std::vector<std::pair<std::string, std::string>> Settings::m_settings =
 long Settings::string_to_long(const std::string &intstr) {
 	try {
 		return std::stol(intstr);
-	} catch (std::invalid_argument &e) {
+	} catch (const std::invalid_argument &e) {
 		throw Exception("error parsing as integer: " + intstr);
 	}
 }

usql/table.cpp

@@ -183,7 +183,7 @@ void Table::commit_row(Row &row) {
 	try {
 		validate_row(row);
 		index_row(row);
-	} catch (Exception &e) {
+	} catch (const Exception &e) {
 		throw e;
 	}
 }

usql/usql.cpp

@@ -11,7 +11,7 @@ std::unique_ptr<Table> USql::execute(const std::string &command) {
 		std::unique_ptr<Node> node = m_parser.parse(command);
 		return execute(*node);
 
-	} catch (std::exception &e) {
+	} catch (const std::exception &e) {
 		return create_stmt_result_table(-1, e.what(), 0);
 	}
 

usql/usql_function.cpp

@@ -82,8 +82,7 @@ std::unique_ptr<ValueNode> USql::pp_function(const std::vector<std::unique_ptr<V
 	return std::make_unique<StringValueNode>(parsed_value->getStringValue());
 }
 
-std::unique_ptr<ValueNode>
-USql::max_function(const std::vector<std::unique_ptr<ValueNode>> &evaluatedPars, const ColDefNode *col_def_node, ColValue *agg_func_value) {
+std::unique_ptr<ValueNode> USql::max_function(const std::vector<std::unique_ptr<ValueNode>> &evaluatedPars, const ColDefNode *col_def_node, ColValue *agg_func_value) {
 	if (col_def_node->type == ColumnType::integer_type || col_def_node->type == ColumnType::date_type) {
 		if (!evaluatedPars[0]->isNull()) {
 			auto val = evaluatedPars[0]->getIntegerValue();