Add -t to specify login script timeout.
Add -w to specify retry wait time.
Describe -p option.
Now understand several -s sections (for several host phone numbers).
Remove -F sw (software flow control), it is impossible with slip.
Change -F hw (hardware flow control) option to -h as in slattach,
we don't need option with argument for only one case.
Call downscript on SIGTERM.
Improve debug diagnostic.
Allow startslip work with several slip lines without killing each other.
Unlink pid file on exit.
Skip \r and \0 in login script parsing instead making them \n.
Use absolute path to default script (/sbin/ifconfig).
Call up/down script in background to prevent hang on them.
