Add asciidoctor package (#3757)

packages/asciidoctor.rb

+require 'package'
+
+class Asciidoctor < Package
+  description 'A fast text processor & publishing toolchain for converting AsciiDoc to HTML5, DocBook & more.'
+  homepage 'https://asciidoctor.org/'
+  version '2.0.10'
+  source_url 'https://github.com/asciidoctor/asciidoctor/archive/v2.0.10.tar.gz'
+  source_sha256 'afca74837e6d4b339535e8ba0b79f2ad00bd1eef78bf391cc36995ca2e31630a'
+
+  binary_url ({
+  })
+  binary_sha256 ({
+  })
+
+  def self.install
+    FileUtils.mkdir_p "#{CREW_DEST_PREFIX}/bin"
+    FileUtils.mkdir_p "#{CREW_DEST_PREFIX}/share/asciidoctor"
+    FileUtils.cp_r Dir.glob('*'), "#{CREW_DEST_PREFIX}/share/asciidoctor"
+    system "install -Dm644 man/asciidoctor.1 #{CREW_DEST_PREFIX}/share/man/man1/asciidoctor.1"
+    FileUtils.ln_s "#{CREW_PREFIX}/share/asciidoctor/bin/asciidoctor", "#{CREW_DEST_PREFIX}/bin/asciidoctor"
+  end
+end