add astropy>=0.4.1 as a requirement

commentary for intermediate commits:
add >0.4.1 to setup.py

apparenty requires can't have versions?

remove setup_requires; I didn't actually know what it did

Author: keflavich

pip-requirements

@@ -1,5 +1,5 @@
 numpy>=1.4.0
-astropy
+astropy>=0.4.1
 requests
 keyring
 beautifulsoup4

setup.py

@@ -100,14 +100,16 @@
                     os.path.relpath(root, PACKAGENAME), filename))
 package_info['package_data'][PACKAGENAME].extend(c_files)
 
+required_packages = ['astropy>=0.4.1', 'requests', 'keyring', 'beautifulsoup4',
+                     'html5lib']
+
 setup(name=PACKAGENAME,
       version=VERSION,
       description=DESCRIPTION,
       scripts=scripts,
       requires=['astropy', 'requests', 'keyring', 'beautifulsoup4',
                 'html5lib'],
-      install_requires=['astropy', 'requests', 'keyring', 'beautifulsoup4',
-                        'html5lib'],
+      install_requires=required_packages,
       include_package_data=True,
       provides=[PACKAGENAME],
       license=LICENSE,