Introduce rc/tmux.kak

This commit adds a kak script dedicated to tmux support, and declares
new command to interact with the current tmux session. Users are now
able to create vertical panes or horizontal panes arbitrarily (as
opposed to setting the `termcmd` variable to the proper command). The
script also has its own `focus` function, used to jump from a  pane to
another.

rc/tmux.kak

@@ -0,0 +1,71 @@
+# http://tmux.github.io/
+# ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+
+## Can be one of "horizontal", "vertical" or "window"
+## When a new client is created, an horizontal pane, a vertical pane or a window will respectively be made
+decl str tmux_default_direction "horizontal"
+
+## The default behaviour for the `new` command is to open an horizontal pane in a tmux session
+hook global KakBegin .* %{
+    %sh{
+        if [ -n "$TMUX" ]; then
+            tmuxcmd=""
+
+            case "${kak_opt_tmux_default_direction}" in
+                vertical) tmuxcmd="tmux split-window -v";;
+                window) tmuxcmd="tmux new-window";;
+                horizontal) tmuxcmd="tmux split-window -h";;
+                *) echo "invalid value: ${kak_opt_tmux_default_direction}" >&2;;
+            esac
+
+            if [ -n "${tmuxcmd}" ]; then
+                echo "set global termcmd '${tmuxcmd}'"
+            fi
+
+            echo "alias global focus focus-tmux"
+        fi
+    }
+}
+
+## Temporarily override the default client creation command
+def -hidden -shell-params tmux_override_termcmd %{
+    %sh{
+        if [ -z "$TMUX" ]; then
+            echo "echo -color Error This command is only available in a tmux session"
+        else
+            readonly cmd_override="$1"
+            readonly termcmd="${kak_opt_termcmd}"
+
+            shift
+            echo "
+                set current termcmd '${cmd_override}'
+                eval new $@
+                set current termcmd '${termcmd}'
+            "
+        fi
+    }
+}
+
+def tmux-new-vertical -shell-params -command-completion -docstring "Create a new vertical pane in tmux" %{
+    %sh{
+        echo "eval %{tmux_override_termcmd 'tmux split-window -v' $@}"
+    }
+}
+
+def tmux-new-horizontal -shell-params -command-completion -docstring "Create a new horizontal pane in tmux" %{
+    %sh{
+        echo "eval %{tmux_override_termcmd 'tmux split-window -h' $@}"
+    }
+}
+
+def -docstring "focus given client" \
+    -shell-params -client-completion \
+    focus-tmux %{ %sh{
+    if [ $# -gt 1 ]; then
+        echo "echo -color Error 'too many arguments, use focus [client]'"
+    elif [ $# -eq 1 ]; then
+        echo "eval -client '$1' focus"
+    elif [ -n "${kak_client_env_TMUX}" ]; then
+        TMUX="${kak_client_env_TMUX}" tmux select-pane -t "${kak_client_env_TMUX_PANE}" > /dev/null
+    fi
+} }