mariadb_get_charset_by_nr is not documented

The function is not documented even though it is required to correctly interpret the character lenghts of fields (e.g. VARCHAR(10) with utf8mb4). Similarly, the types it uses are not documented.

The presence of MYSQL_FIELD::charsetnr is not indicated in the documentation.

The type used with mariadb_get_infov() for MARIADB_CONNECTION_CHARSET_INFO is also not documented: const *MY_CHARSET_INFO

The documentation that was used was the connector-c wiki :https://github.com/mariadb-corporation/mariadb-connector-c/wiki/