Install crontab w/ script

This adds a couple of new scripts: install-crontab.sh and update.sh. The
install-crontab script does exactly that -- it installs a new crontab
that runs the update script every 5 minutes. An update script was added
to simplify the crontab a bit and to ensure the Elixir update script is
executed from the correct directory.

install-crontab.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+# Install crontab to run update script
+
+SCRIPT_DIR="$(builtin cd "$(dirname "${BASH_SOURCE[0]}")" && pwd -P)"
+
+(crontab -l 2>/dev/null; echo "*/5 * * * * $SCRIPT_DIR/update.sh") | crontab -

update.exs

@@ -6,7 +6,7 @@ defmodule Instances do
 
   def init() do
     File.rename(@update_file, "#{@update_file}-prev")
-    update
+    update()
   end
 
   def request(url) do

update.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+SCRIPT_DIR="$(builtin cd "$(dirname "${BASH_SOURCE[0]}")" && pwd -P)"
+
+cd "$SCRIPT_DIR"
+mix run update.exs