💥 Remove :feature category

:feature was a "catch-all" category. Many of its modules fit better in
other categories, so they've been moved:

- feature/debugger -> tools/debugger
- feature/evil -> editor/evil
- feature/eval -> tools/eval
- feature/lookup -> tools/lookup
- feature/snippets -> editor/snippets
- feature/file-templates -> editor/file-templates
- feature/workspaces -> ui/workspaces

More potential changes in the future:

- A new :term category for terminal emulation modules (eshell, term and
  vterm).
- A new :os category for modules dedicated to os-specific functionality.
  The :tools macos module would fit here, but so would modules for nixos
  and arch.
- A new :services category for web-service integration, like wakatime,
  twitter, elfeed, gist and pastebin services.

modules/tools/eval/autoload/settings.el

@@ -0,0 +1,58 @@
+;;; tools/eval/autoload/settings.el -*- lexical-binding: t; -*-
+
+;;
+;; REPLs
+
+;;;###autoload
+(defvar +eval-repls nil
+  "An alist mapping major modes to plists that describe REPLs. Used by
+`+eval/open-repl-other-window' and filled with the `:repl' setting.")
+
+;;;###autodef
+(defun set-repl-handler! (modes command)
+  "Defines a REPL for MODES.
+
+MODES is either a single major mode symbol or a list of them. COMMAND is a
+function that creates and returns the REPL buffer.
+
+COMMAND can either be a function that takes no arguments, or an interactive
+command that will be called interactively."
+  (dolist (mode (doom-enlist modes))
+    (setf (alist-get mode +eval-repls) command)))
+
+
+;;
+;; Evaluation
+
+;;;###autoload
+(defvar +eval-runners nil
+  "Alist mapping major modes to interactive runner functions.")
+
+;;;###autodef
+(defun set-eval-handler! (mode command)
+  "Define a code evaluator for major mode MODE with `quickrun'.
+
+1. If MODE is a string and COMMAND is the string, MODE is a file regexp and
+   COMMAND is a string key for an entry in `quickrun-file-alist'.
+2. If MODE is not a string and COMMAND is a string, MODE is a major-mode symbol
+   and COMMAND is a key (for `quickrun--language-alist'), and will be registered
+   in `quickrun--major-mode-alist'.
+3. If MODE is not a string and COMMAND is an alist, see `quickrun-add-command':
+   (quickrun-add-command MODE COMMAND :mode MODE).
+4. If MODE is not a string and COMMANd is a symbol, add it to
+   `+eval-runners', which is used by `+eval/region'."
+  (declare (indent defun))
+  (cond ((symbolp command)
+         (push (cons mode command) +eval-runners))
+        ((stringp command)
+         (after! quickrun
+           (push (cons mode command)
+                 (if (stringp mode)
+                     quickrun-file-alist
+                   quickrun--major-mode-alist))))
+        ((listp command)
+         (after! quickrun
+           (quickrun-add-command
+             (or (cdr (assq mode quickrun--major-mode-alist))
+                 (string-remove-suffix "-mode" (symbol-name mode)))
+             command :mode mode)))))