Integration with GNU screen; based on tmux.kak

- Hack: kak sets `/proc/self/fd/0 -> /dev/null`. Get the client process tty because Screen needs to know the controlling terminal. Else Screen will use the last known tty and will open new windows on a different terminal if one is connected.

rc/base/screen.kak

@@ -0,0 +1,50 @@
+# http://gnu.org/software/screen/
+# ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+ 
+hook global KakBegin .* %{
+    %sh{
+        [ -z "kak_client_env_$STY" ] && exit
+        echo "
+            alias global focus screen-focus
+            alias global new screen-new-vertical
+        "
+    }
+}
+
+
+def screen-new-vertical -params .. -command-completion -docstring "Create a new vertical region" %{
+     %sh{
+
+        tty="$(ps -o tty ${kak_client_pid} | tail -n 1)"
+        screen -X eval 'split -h' 'focus down' "screen kak -c \"${kak_session}\" -e \"$*\"" < "/dev/$tty"
+    }
+}
+
+def screen-new-horizontal -params .. -command-completion -docstring "Create a new horizontal region" %{
+     %sh{
+        tty="$(ps -o tty ${kak_client_pid} | tail -n 1)"
+        screen -X eval 'split -v' 'focus right' "screen kak -c \"${kak_session}\" -e \"$*\"" < "/dev/$tty"
+    }
+}
+
+def screen-new-window -params .. -command-completion -docstring "Create a new window" %{
+    %sh{
+        tty="$(ps -o tty ${kak_client_pid} | tail -n 1)"
+        screen -X screen kak -c "${kak_session}" -e "$*" < "/dev/$tty"
+    }
+}
+
+def -docstring %{screen-focus [<client>]: focus the given client
+If no client is passed then the current one is used} \
+    -params ..1 -client-completion \
+    screen-focus %{ %sh{
+        if [ $# -eq 1 ]; then
+            printf %s\\n "
+                evaluate-commands -client '$1' %{ %sh{
+                    screen -X focus
+            }}"
+        elif [ -n "kak_client_env_$STY" ]; then
+            tty="$(ps -o tty ${kak_client_pid} | tail -n 1)"
+            screen -X select "$kak_client_env_WINDOW" < "$/dev/$tty"
+        fi
+} }