new package: py-numcodecs (#14330)

* new package: py-numcodecs

* make msgpack variant

var/spack/repos/builtin/packages/py-numcodecs/package.py

+# Copyright 2013-2019 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 PyNumcodecs(PythonPackage):
+    """Numcodecs is a Python package providing buffer compression and
+    transformation codecs for use in data storage and communication
+    applications.
+    """
+
+    homepage = "https://github.com/zarr-developers/numcodecs"
+    url      = "https://pypi.io/packages/source/n/numcodecs/numcodecs-0.6.4.tar.gz"
+
+    version('0.6.4', sha256='ef4843d5db4d074e607e9b85156835c10d006afc10e175bda62ff5412fca6e4d')
+
+    variant('msgpack', default=False, description='Codec to encode data as msgpacked bytes.')
+
+    depends_on('py-setuptools@18.0:',       type='build')
+    depends_on('py-setuptools-scm@1.5.4:',  type=('build', 'run'))
+    depends_on('py-numpy@1.7:',             type=('build', 'run'))
+    depends_on('py-msgpack', type=('build', 'run'), when='+msgpack')