New bin/doom (eventual replacement for make)

This commit adds bin/doom, which acts as the middle man that make once
was (and will stay for a while, though the documentation will shift away
from using it). It does everything the previous make interface did, but
is faster and more flexible. bin/doom should eventually replace the
makefile.

bin/doom also makes it easier to run Doom outside of ~/.emacs.d and
~/.doom.d with, for example:

  bin/doom run -p ~/.other.doom.d/ -e ~/.other.emacs.d

bin/doom.cmd is included for Windows users, but I don't recommend using
it yet. It hasn't been tested nor have I ever written a batch script
before.

Also update init.example.el with new defaults.

init.el

@@ -27,4 +27,9 @@
 ;;
 ;;; License: MIT
 
+(setq user-emacs-directory (file-name-directory load-file-name)
+      load-prefer-newer noninteractive)
+
 (require 'core (concat user-emacs-directory "core/core"))
+(when noninteractive
+  (require 'core-dispatcher))