dev: redesign .gitignore

Be more selective about what gets ignored, and permit arbitrary *.el
files in case the user is using $EMACSDIR as their $DOOMDIR.

.gitignore

@@ -1,21 +1,25 @@
-# generated by macOS
-.DS_Store
+# project dotfiles
+.*
+!.doom*
+!.dir-locals.el
+!.gitignore
+!/.github
 
-# machine generated doom profiles or metadata
+# generated by doom
 /profiles/*.el
 /.local*/
 
-# possible user config files
-/profiles.el
-/init.el
-/config.el
-/packages.el
+# possible user config files (if $DOOMDIR == $EMACSDIR)
+/*.el
+!/early-init.el
+/user-lisp/
+/themes/
+/snippets/
 
-# generated by elisp packages in sub-directories
+# generated by elisp packages
+\#*
 *~
 *.*~
-\#*
-.\#*
 *.cache*
 *.log
 *.elc
@@ -27,18 +31,7 @@
 *.rel
 *_archive
 *_flymake.*
-.dap-breakpoints
-.emacs.desktop
-.emacs.desktop.lock
-.org-id-locations
-.projectile
-.tern-port
-.yas-compiled-snippets.el
 flycheck_*.el
-
-# generated by elisp packages at root
-/.local/
-/.cask/
 /auto/
 /auto-save-list/
 /cask/