Add SP_ERR_MEM failure code.
Always return an empty port list unless allocation fails.
Identify ports by sp_port structure, not name.
Handle conversion of unicode names to char * on Windows.
Port name string length now no longer needs to be passed around.
Add sp_get_port_by_name() function.
Make sp_list_ports and sp_get_port_by_name return int.
Add sp_free_port() function.
Update documentation.
Clarify documentation for sp_read() and sp_write().