update README
use Text::Table to list host either
Model->all(\&closure) works like map on all Model instance
Host#hash() generate hash for rendering template
$self->actor("ActorName") is a global helper
"Model::Host#hash()"-compatible template of Actor::Nginx
apply all(\&closure) in Command::List::*
Model#columns returns all names of columns
implement Model#slice()
Host has fullname, address, port
must die if failing to remove
remove all backends belong to the host deleting