package: add asciidoctor gem (#9905)

* package: add asciidoctor gem

Faster, easier to use, less impossible to install correctly
implementation of asciidoc.

* ritual sacrifice of EOF whitespace to flake8

var/spack/repos/builtin/packages/asciidoctor/package.py

@@ -0,0 +1,20 @@
+# Copyright 2013-2018 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class Asciidoctor(Package):
+    """Modern asciidoc tool based on ruby"""
+
+    homepage = "https://asciidoctor.org/"
+    url      = "https://rubygems.org/downloads/asciidoctor-1.5.8.gem"
+
+    version('1.5.8', '5f55200cab8d1cfcf561e66d3f477159', expand=False)
+
+    extends('ruby')
+
+    def install(self, spec, prefix):
+        gem('install', 'asciidoctor-{0}.gem'.format(self.version))