💥 Replace core-popup with new feature/popup module

This is a breaking change! Update your :popup settings. Old ones will
throw errors!

Doom's new popup management system casts off its shackles (hur hur) and
replaces them with the monster that is `display-buffer-alist`, and
window parameters.

However, this is highly experimental! Expect edge cases.  Particularly
with org-mode and magit (or anything that does its own window
management).

Relevant to #261, #263, #325

modules/tools/gist/config.el

@@ -7,7 +7,6 @@
 (def-package! gist
   :commands (gist-list gist-region-or-buffer-private gist-region-or-buffer)
   :config
-  (set! :popup "*github:gists*" :size 15 :select t :autokill t)
   (set! :evil-state 'gist-list-mode 'normal)
 
   (defun +gist*list-render (orig-fn &rest args)