Add package for httpie (#3609)

* Add package for httpie

* Remove wayward FIXME and flake8 cleanup

* Update dependencies, address PR feedback

Fine tune dependencies (version constraints).
Add missing dependency.
Make SOCKS support a variant.

* Flake8 cleanup

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

+##############################################################################
+# Copyright (c) 2013-2016, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/llnl/spack
+# Please also see the LICENSE file for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License (as
+# published by the Free Software Foundation) version 2.1, February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+
+class Httpie(PythonPackage):
+    """Modern command line HTTP client."""
+
+    homepage = "https://httpie.org/"
+    url      = "https://pypi.io/packages/source/h/httpie/httpie-0.9.8.tar.gz"
+
+    version('0.9.8', 'e0d1af07d0959a2e081e7954797ce260')
+
+    variant('socks', default=True,
+            description='Enable SOCKS proxy support')
+
+    depends_on('py-setuptools', type=('build', 'run'))
+    depends_on('py-pygments@2.1.3:', type=('build', 'run'))
+    depends_on('py-requests@2.11.0:', type=('build', 'run'))
+    depends_on('py-pysocks', type=('build', 'run'), when="+socks")
+    depends_on('py-argparse@1.2.1:', type=('build', 'run'), when='^python@:2.6,3.0:3.1')