Fix broken syscalls

The syscall interfaces seem to have changed since whenever this package
was written.
Fix error message

The syscall causing the error here is FCNTL, not IOCTL.
Support non-standard baud rates

This sets the baud rate using the IOSSIOSPEED ioctl, rather than as part
of the termios options, which allows arbitrary speeds.
Merge branch 'fix_for_go12'
Merge branch 'nonstandard_baud_rates'