Update to sphinx >= 1.7.0

- Make the fixes suggested here so our docs become compatible with
  sphinx 1.7.0:
  sphinx-doc/sphinx#4609 (comment)

- Upgrade to sphinx 1.7.0

Author: njsmith

ci/rtd-requirements.txt

@@ -1,5 +1,4 @@
 # RTD is currently installing 1.5.3, which has a bug in :lineno-match:
-# 1.7.0 hits https://github.com/sphinx-doc/sphinx/issues/4609
-sphinx == 1.6.7
+sphinx >= 1.7.0
 sphinx_rtd_theme
 sphinxcontrib-trio

docs/source/conf.py

@@ -28,11 +28,13 @@
 nitpicky = True
 # Except for these ones, which we expect to point to unknown targets:
 nitpick_ignore = [
-    ("py:obj", "CapacityLimiter-like object"),
-    ("py:obj", "bytes-like"),
+    ("py:class", "CapacityLimiter-like object"),
+    ("py:class", "bytes-like"),
+    ("py:class", "None"),
     # trio.abc is documented at random places scattered throughout the docs
     ("py:mod", "trio.abc"),
 ]
+autodoc_inherit_docstrings = False
 
 # XX hack the RTD theme until
 #   https://github.com/rtfd/sphinx_rtd_theme/pull/382