Delay import of Sphinx (#248)

* Delay import of Sphinx

* ENH: do not import Sphinx unless it has already been imported

* Delay import of Sphinx

(cherry picked from commit 4978673)

numpydoc/docscrape.py

@@ -16,7 +16,6 @@
 import copy
 import sys
 
-from sphinx.ext.autodoc import ALL
 
 def strip_blank_lines(l):
     "Remove leading and trailing blank lines from a list of lines"
@@ -626,6 +625,11 @@ def __init__(self, cls, doc=None, modulename='', func_doc=FunctionDoc,
             raise ValueError("Expected a class or None, but got %r" % cls)
         self._cls = cls
 
+        if 'sphinx' in sys.modules:
+            from sphinx.ext.autodoc import ALL
+        else:
+            ALL = object()
+
         self.show_inherited_members = config.get(
                     'show_inherited_class_members', True)