Basic conversions

The following table lists the C++ types for which quince_postgresql provides basic conversions. So these are the types T for which quince_postgresql allows direct_mapper<T>. The table also shows the SQL types to which they are converted.

C++ mapped type	SQL type from quince_postgresql's basic conversion
`bool`	`boolean`
`int16_t`	`smallint`
`int32_t`	`integer`
`int64_t`	`bigint`
`serial`	`bigserial`
`float`	`real`
`double`	`double precision`
`std::string`	`text`
`std::vector<uint8_t>`	`bytea`
`quince::timestamp` ^[a]	`timestamp`
^[a] The C++ type `quince::timestamp` is a trivial wrapper over `std::string`.