Support Vim, Tmux, Emacs with Stow

After moving off of Meta, Dotfiles has a greater responsibility to
manage configs. Vim, Tmux, and Emacs are now within Stow's purview.

configs/shared/emacs/.emacs.d/snippets/rjsx-mode/const-function

@@ -0,0 +1,7 @@
+# -*- mode: snippet -*-
+# name: const function
+# key: cfn
+# --
+const $1 = ($2) => {
+  $3
+}