doc: Improve docs for ssh_channel_get_exit_status().
doc: Improve docs for ssh_channel_get_exit_status().

BUG: https://red.libssh.org/issues/154

wangshawn/libssh,mwgoldsmith/libssh,sebadoom/libssh,mwgoldsmith/ssh,robxu9/libssh,sebadoom/libssh,taikoo/libssh,kedazo/libssh,DouglasHeriot/libssh,nviennot/libssh,sebadoom/libssh,DouglasHeriot/libssh,wangshawn/libssh,taikoo/libssh,nviennot/libssh,sebadoom/libssh,mwgoldsmith/ssh,wangshawn/libssh,kedazo/libssh,wangshawn/libssh,nviennot/libssh,Distrotech/libssh,pouete/libssh,elastichosts/libssh,mwgoldsmith/ssh,kedazo/libssh,robxu9/libssh,mwgoldsmith/libssh,elastichosts/libssh,elastichosts/libssh,DouglasHeriot/libssh,mwgoldsmith/ssh,kedazo/libssh,Distrotech/libssh,nviennot/libssh,mwgoldsmith/libssh,pouete/libssh,taikoo/libssh,Distrotech/libssh,Distrotech/libssh,mwgoldsmith/libssh,taikoo/libssh,pouete/libssh,pouete/libssh,robxu9/libssh,robxu9/libssh,DouglasHeriot/libssh