capnproto: New package. (#14557)

* capnproto: New package.

* capnproto: Fix flake8 errors.

* Remove characters invalid in Python 2.

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

+# Copyright 2013-2020 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 Capnproto(AutotoolsPackage):
+    """Cap'n Proto is an insanely fast data interchange
+    format and capability-based RPC system.
+    """
+
+    homepage = "https://capnproto.org/"
+    url      = "https://capnproto.org/capnproto-c++-0.7.0.tar.gz"
+    git      = "https://github.com/capnproto/capnproto"
+
+    version('0.7.0', sha256='c9a4c0bd88123064d483ab46ecee777f14d933359e23bff6fb4f4dbd28b4cd41')
+
+    def configure_args(self):
+        return ['--without-openssl']