Add libtool (2.4.6) package

This adds GNU libtool as a package in preparation for a libusb package.

Tested as working properly on Samsung XE50013-K01US.

packages/libtool.rb

+require 'package'
+
+class Libtool < Package
+  version '2.4.6'
+  source_url 'https://ftp.gnu.org/gnu/libtool/libtool-2.4.6.tar.gz'
+  source_sha1 '25b6931265230a06f0fc2146df64c04e5ae6ec33'
+
+  depends_on 'buildessential'
+
+  def self.build
+    system "./configure"
+    system "make"
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end