sqlpp::optional is an alias for std::optional for C++17 and beyond.
Otherwise, it is a simple and incomplete backport.
For older versions of C++, the library offers simple back
Similar for string_view and span.
Add support for connection pooling
* Add support for connection pooling to the core code.
* Add support for PostgreSQL connection pooling with tests.
* Add support for SQLite3 connection pooling with tests.
* Add support for MySQL connection pooling with tests.