Introduce general.el & rewrite map!

+ Now uses an overriding keymap for leader keys, so that it is always
  available, even outside of normal/visual states. In insert/emacs
  states, or in sessions where evil is absent, an alternative prefix is
  used for leader/localleader keys. See these variables:
  + doom-leader-prefix
  + doom-leader-alt-prefix
  + doom-localleader-prefix
  + doom-localleader-alt-prefix
+ Keybinds now support alternative prefixes through the new :alt-prefix
  property. This is useful for non-evil users and non-normal evil
  states. By default, this is M-SPC (leader) and M-SPC m (localleader).
+ Removed +evil-commands flag from config/default (moved to
  feature/evil/+commands.el).
+ config/default/+bindings.el has been split into
  config/default/+{evil,emacs}-bindings.el, which one is loaded depends
  on whether evil is present or not. The latter is blank, but will soon
  be populated with a keybinding scheme for non-evil users (perhaps
  inspired by #641).
+ The define-key! macro has been replaced; it is now an alias for
  general-def.
+ Added unmap! as an alias for general-unbind.
+ The following modifier key conventions are now enforced for
  consistency, across all OSes:
    alt/option      = meta
    windows/command = super
  It used to be
    alt/option      = alt
    windows/command = meta
  Many of the default keybinds have been updated to reflect this switch,
  but it is likely to affect personal meta/super keybinds!

The map! macro has also been rewritten to use general-define-key. Here
is what has been changed:

+ map! no longer works with characters, e.g. (map! ?x #'do-something) is
  no longer supported. Keys must be kbd-able strings like "C-c x" or
  vectors like [?C-c ?x].
+ The :map and :map* properties are now the same thing. If specified
  keymaps aren't defined when binding keys, it is automatically
  deferred.
+ The way you bind local keybinds has changed:

    ;; Don't do this
    (map! :l "a" #'func-a
          :l "b" #'func-b)
    ;; Do this
    (map! :map 'local "a" #'func-a
                      "b" #'func-b)

+ map! now supports the following new blocks:
  + (:if COND THEN-FORM ELSE-FORM...)
  + (:alt-prefix PREFIX KEYS...) -- this prefix will be used for
    non-normal evil states. Equivalent to :non-normal-prefix in general.
+ The way you declare a which-key label for a prefix key has changed:

    ;; before
    (map! :desc "label" :prefix "a" ...)
    ;; now
    (map! :prefix ("a" . "label") ...)

+ It used to be that map! supported binding a key to a key sequence,
  like so:

    (map! "a" [?x])  ; pressing a is like pressing x

  This functionality was removed *temporarily* while I figure out the
  implementation.

Addresses: #448, #814, #860
Mentioned in: #940

modules/emacs/eshell/config.el

@@ -123,33 +123,30 @@ You should use `det-eshell-alias!' to change this.")
   (defun +eshell|init-keymap ()
     "Setup eshell keybindings. This must be done in a hook because eshell-mode
 redefines its keys every time `eshell-mode' is enabled."
-    (when (featurep 'evil)
-      (evil-define-key* 'normal eshell-mode-map
-        [return]   #'+eshell/goto-end-of-prompt
-        "c"        #'+eshell/evil-change
-        "C"        #'+eshell/evil-change-line
-        "d"        #'+eshell/evil-delete
-        "D"        #'+eshell/evil-delete-line)
-      (evil-define-key* 'insert eshell-mode-map
-        [tab]      #'+eshell/pcomplete
-        "\C-j"     #'evil-window-down
-        "\C-k"     #'evil-window-up
-        "\C-h"     #'evil-window-left
-        "\C-l"     #'evil-window-right
-        "\C-d"     #'+eshell/quit-or-delete-char
-        "\C-p"     #'eshell-previous-input
-        "\C-n"     #'eshell-next-input))
-    (define-key! eshell-mode-map
-      (kbd "C-s")   #'+eshell/search-history
-      (kbd "C-c s") #'+eshell/split-below
-      (kbd "C-c v") #'+eshell/split-right
-      (kbd "C-c x") #'+eshell/kill-and-close
-      [remap split-window-below]  #'+eshell/split-below
-      [remap split-window-right]  #'+eshell/split-right
-      [remap doom/backward-to-bol-or-indent] #'eshell-bol
-      [remap doom/backward-kill-to-bol-and-indent] #'eshell-kill-input
-      [remap evil-window-split]   #'+eshell/split-below
-      [remap evil-window-vsplit]  #'+eshell/split-right))
+    (map! :map eshell-mode-map
+          :n [return]   #'+eshell/goto-end-of-prompt
+          :n "c"        #'+eshell/evil-change
+          :n "C"        #'+eshell/evil-change-line
+          :n "d"        #'+eshell/evil-delete
+          :n "D"        #'+eshell/evil-delete-line
+          :i [tab]      #'+eshell/pcomplete
+          :i "C-j"     #'evil-window-down
+          :i "C-k"     #'evil-window-up
+          :i "C-h"     #'evil-window-left
+          :i "C-l"     #'evil-window-right
+          :i "C-d"     #'+eshell/quit-or-delete-char
+          :i "C-p"     #'eshell-previous-input
+          :i "C-n"     #'eshell-next-input
+          "C-s"   #'+eshell/search-history
+          "C-c s" #'+eshell/split-below
+          "C-c v" #'+eshell/split-right
+          "C-c x" #'+eshell/kill-and-close
+          [remap split-window-below]  #'+eshell/split-below
+          [remap split-window-right]  #'+eshell/split-right
+          [remap doom/backward-to-bol-or-indent] #'eshell-bol
+          [remap doom/backward-kill-to-bol-and-indent] #'eshell-kill-input
+          [remap evil-window-split]   #'+eshell/split-below
+          [remap evil-window-vsplit]  #'+eshell/split-right))
   (add-hook 'eshell-first-time-mode-hook #'+eshell|init-keymap))