Add axel package

Add pre-built binaries

packages/axel.rb

+require 'package'
+
+class Axel < Package
+  description 'Light command line download accelerator for Linux and Unix'
+  homepage 'https://github.com/axel-download-accelerator/axel'
+  version '2.16.1'
+  source_url 'https://github.com/axel-download-accelerator/axel/releases/download/v2.16.1/axel-2.16.1.tar.xz'
+  source_sha256 'd34094eb63eaebc989f96eabdda091dcfb28e840bb8d274a5f216775941f59e4'
+
+  binary_url ({
+    aarch64: 'https://dl.bintray.com/chromebrew/chromebrew/axel-2.16.1-chromeos-armv7l.tar.xz',
+     armv7l: 'https://dl.bintray.com/chromebrew/chromebrew/axel-2.16.1-chromeos-armv7l.tar.xz',
+       i686: 'https://dl.bintray.com/chromebrew/chromebrew/axel-2.16.1-chromeos-i686.tar.xz',
+     x86_64: 'https://dl.bintray.com/chromebrew/chromebrew/axel-2.16.1-chromeos-x86_64.tar.xz',
+  })
+  binary_sha256 ({
+    aarch64: '823600341cf335d42a3e23465d693925e1b03af01aa974f52e3ca66659c0e91b',
+     armv7l: '823600341cf335d42a3e23465d693925e1b03af01aa974f52e3ca66659c0e91b',
+       i686: '2f3807501995381c3c60beff7eb30bc007337a7f28fc0fd244aea9a3a046fc72',
+     x86_64: '842d5fee9613e55a6efc696739814a623d77b16494d2bf7c6d473aa5b686530c',
+  })
+
+  def self.build
+    system "./configure --prefix=#{CREW_PREFIX}"
+    system 'make'
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end