Add API for and default handler for debug messages.
Add debug macros.
Add debug output for all entry and exit points.
Add additional debug messages.
Additional argument checking.
Generate debug output when returning using TRY() macro.
Return SP_ERR_SUPP from sp_list_ports() on unsupported platforms.
Fix swapped DCD & RI signals on Windows.
Add back previously deleted sp_get_config function.
Make port structure opaque.
Add sp_get_port_handle() function.
Clarify documentation.
Make configuration structure opaque.
Add generator program for configuration accessor headers.
Initialise structure in sp_new_config().
Fix bug in debug message generation in sp_flush().
Handle -EAGAIN in non-blocking reads on Unix, and return 0 from sp_read().
Fix SET_FAIL macro.
Implement non-blocking I/O on Windows.
Windows nonblocking write: 1 byte at a time to know when buffer fills.