new package: py-arrow (#13575)

* new package: py-arrow

* actually use dependencies from 0.14.7 not from current HEAD

* drop dependencies that dont appear in the source

* readd sphinx as doc dependency

* update dependencies

* drop doc-only dependencies

var/spack/repos/builtin/packages/py-arrow/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 PyArrow(PythonPackage):
+    """Arrow is a Python library that offers a sensible and human-friendly
+    approach to creating, manipulating, formatting and converting dates,
+    times and timestamps. It implements and updates the datetime type,
+    plugging gaps in functionality and providing an intelligent module API
+    that supports many common creation scenarios. Simply put, it helps you
+    work with dates and times with fewer imports and a lot less code."""
+
+    homepage = "https://arrow.readthedocs.io/en/latest/"
+    url      = "https://pypi.io/packages/source/a/arrow/arrow-0.14.7.tar.gz"
+
+    version('0.14.7', sha256='67f8be7c0cf420424bc62d8d7dc40b44e4bb2f7b515f9cc2954fb36e35797656')
+
+    depends_on('python@2.7:2.8,3.5:', type=('build', 'run'))
+    depends_on('py-setuptools', type='build')
+    depends_on('py-backports-functools_lru_cache@1.2.1:', type=('build', 'run'), when='^python@2.7:2.8')
+    depends_on('py-python-dateutil', type=('build', 'run'))
+    depends_on('py-chai', type='test')
+    depends_on('py-mock', type='test')
+    depends_on('py-pytz@2019.0:', type='test')