fix setup.py to get documentation to build under CircleCI (#2650)

setup.py

@@ -268,15 +268,37 @@ def finalize_options(self):
 
 linux_testenv = win_testenv[:]
 
+#
+# This list partially duplicates requirements_docs.txt.
+# The main difference is that we don't include version pins here unless
+# absolutely necessary, whereas requirements_docs.txt includes pins for
+# everything, by design.
+#
+# For more info about the difference between the two:
+#
+#   https://packaging.python.org/discussions/install-requires-vs-requirements/
+#
 docs_testenv = linux_testenv + distributed_env + [
     'sphinx',
     'sphinxcontrib-napoleon',
     'plotly',
-    'pattern <= 2.6',
+    #
+    # Pattern is a PITA to install, it requires mysqlclient, which in turn
+    # requires MySQL dev tools be installed.  We don't need it for building
+    # documentation.
+    #
+    # 'Pattern==3.6',  # Need 3.6 or later for Py3 support
     'sphinxcontrib.programoutput',
     'sphinx-gallery',
     'memory_profiler',
     'annoy',
+    'Pyro4',
+    'scikit-learn',
+    'nltk',
+    'testfixtures',
+    'statsmodels',
+    'pyemd',
+    'pandas',
 ]
 
 if sys.version_info < (3, 7):
@@ -288,18 +310,6 @@ def finalize_options(self):
 if (3, 0) < sys.version_info < (3, 7):
     linux_testenv.extend(['nmslib'])
 
-docs_testenv = linux_testenv + distributed_env + [
-    'sphinx',
-    'sphinxcontrib-napoleon',
-    'plotly',
-    'Pattern >= 3.6',  # Need 3.6 or later for Py3 support
-    'sphinxcontrib.programoutput',
-]
-#
-# Get Py2.7 docs to build, see https://github.com/RaRe-Technologies/gensim/pull/2552
-#
-if sys.version_info == (2, 7):
-    docs_testenv.insert(0, 'doctools==0.14')
 
 ext_modules = [
     Extension('gensim.models.word2vec_inner',