Add configuration for zsh

- Add ~/.zshrc
  + Configure on how the `history` works
  + Enable nicer `cd` and globbing behavior
  + Enable tab completion, and make them feel nicer
  + Enable VI mode and add some VI-like key bindings
- Add ~/.zlogout clearing the screen
- Add ~/.config/zsh/.zshrc and make it dispatch to ~/.zshrc
  to make `zsh` use the same configuration even on more
  recent Debian/Ubuntu machines that do not look for
  ~/.zshrc any more
- Ensure ~/.local/state/zsh/ exists

.config/shell/aliases

@@ -12,9 +12,19 @@ forget() {  # the current history and restore $HISTFILE from disk
     if [ -n "$BASH_VERSION" ]; then
         history -c
         history -r
+    elif [ -n "$ZSH_VERSION" ]; then
+        _histsize=$HISTSIZE
+        HISTSIZE=0  # because shrinking the list to 0 discards all entries
+        HISTSIZE=$_histsize
+        unset _histsize
+        fc -R "$HISTFILE"
     fi
 }
 
+if [ -n "$ZSH_VERSION" ]; then
+    alias forget=' forget'  # Leading space => The invocation itself is forgotten because of `setopt HIST_IGNORE_SPACE`
+fi
+
 
 
 alias path='echo $PATH | tr ":" "\n"'

.config/zsh/.zlogout

@@ -0,0 +1,8 @@
+#!/bin/zsh
+
+# Failsafe: Dispatch to the real `zsh` logout file in ~/
+#
+# See ~/.config/zsh/.zshrc for the details
+
+
+[ -f "$HOME/.zlogout" ] && . "$HOME/.zlogout"

.config/zsh/.zshenv

@@ -0,0 +1,11 @@
+#!/bin/zsh
+
+# Failsafe: Dispatch to the real `zsh` env file in ~/
+#
+# See ~/.config/zsh/.zshrc for the details
+#
+# Without this, a set `$ZDOTDIR` would silently skip ~/.zshenv
+# and lose `skip_global_compinit=1`
+
+
+[ -f "$HOME/.zshenv" ] && . "$HOME/.zshenv"

.config/zsh/.zshrc

@@ -0,0 +1,12 @@
+#!/bin/zsh
+
+# Failsafe: Dispatch to the real `zsh` config file in ~/
+#
+# `zsh` itself only reads `$ZDOTDIR`, which defaults to ~/,
+# and never looks into ~/.config/zsh on its own
+# => This file is dead code unless something sets `$ZDOTDIR`
+#    to this folder (e.g., a future Debian default;
+#    see Debian bug #1036290 for such a proposal)
+
+
+[ -f "$HOME/.zshrc" ] && . "$HOME/.zshrc"

.config/zsh/README.md

@@ -0,0 +1,8 @@
+# `zsh`-related Configurations
+
+This folder is NOT read by `zsh` by default:
+    `zsh` only reads `$ZDOTDIR`, which defaults to ~/.
+
+The files here are failsafes:
+    Should some machine or future distribution set `$ZDOTDIR` to this folder,
+    they dispatch back to the real config files in ~/.