Add zeromq package

ZeroMQ is a high-performance asynchronous messaging library, aimed at
use in distributed or concurrent applications.

Tested as working on Samsung Chromebook Plus (aarch64). All tests pass.

packages/zeromq.rb

+require 'package'
+
+class Zeromq < Package
+  description 'Fast messaging system built on sockets. C and C++ bindings. aka 0MQ, ZMQ.'
+  homepage 'http://zeromq.org/'
+  version '4.2.2'
+  source_url 'https://github.com/zeromq/libzmq/releases/download/v4.2.2/zeromq-4.2.2.tar.gz'
+  source_sha256 '5b23f4ca9ef545d5bd3af55d305765e3ee06b986263b31967435d285a3e6df6b'
+
+  binary_url ({
+  })
+  binary_sha256 ({
+  })
+
+  depends_on 'libunwind'
+  depends_on 'xzutils'
+
+  def self.build
+    system './configure',
+      "--prefix=#{CREW_PREFIX}",
+      "--libdir=#{CREW_LIB_PREFIX}",
+      "--disable-dependency-tracking"
+    system 'make'
+  end
+
+  def self.install
+    system 'make', "DESTDIR=#{CREW_DEST_DIR}", 'install'
+  end
+end