install python-magic-bin in win32 and macOS

setup.py

@@ -3,6 +3,7 @@
 
 from __future__ import unicode_literals
 
+import sys
 import os
 import io
 from setuptools import setup, find_packages
@@ -18,6 +19,11 @@ VERSION = __import__('spirit').__version__
 with io.open(os.path.join(BASE_DIR, 'requirements.txt'), encoding='utf-8') as fh:
     REQUIREMENTS = fh.read()
 
+if sys.platform.startswith(('win32', 'darwin')):
+    PYTHON_MAGIC_DEP = ['python-magic-bin==0.4.14']
+else:  # Linux?
+    PYTHON_MAGIC_DEP = ['python-magic==0.4.15']
+
 # allow setup.py to be run from any path
 os.chdir(os.path.normpath(os.path.join(os.path.abspath(__file__), os.pardir)))
 
@@ -39,7 +45,7 @@ spirit=spirit.extra.bin.spirit:main
     zip_safe=False,
     install_requires=REQUIREMENTS,
     extras_require={
-        'files': ['python-magic==0.4.15']},
+        'files': PYTHON_MAGIC_DEP},
     license='MIT License',
     classifiers=[
         'Development Status :: 5 - Production/Stable',

spirit/core/conf/defaults.py

@@ -67,6 +67,8 @@ ST_ALLOWED_UPLOAD_IMAGE_FORMAT = ('jpeg', 'jpg', 'gif')
 ST_UPLOAD_FILE_ENABLED = True
 #: Uploaded files will be validated against these formats.
 #: This is a map of extension and media-type. Both are used for validation.
+#: Requires running ``pip install django-spirit[files]`` to install
+#: `python-magic <https://github.com/ahupp/python-magic#installation>`_
 #:
 #: .. Note::
 #:     To find a media-type just add an extension and an empty media-type,