build+docs: align minimum requirements with ndn-cxx/NFD

 * Recommend boost >= 1.65.1 and gcc >= 7.4.0
 * Require clang >= 4.0, or Xcode >= 9.0 on macOS
 * Silence an ABI-related diagnostic message from gcc on armv7
 * Update waf to version 2.0.21
 * Make graphviz optional for building documentation
 * Sync sphinx configuration

Change-Id: Ib271da841cd12e7595ae83d75bd0fc681f8c231f
diff --git a/docs/RELEASE-NOTES.rst b/docs/RELEASE-NOTES.rst
index 2a63dae..04e2f84 100644
--- a/docs/RELEASE-NOTES.rst
+++ b/docs/RELEASE-NOTES.rst
@@ -1,4 +1,4 @@
-NLSR Release Notes
-==================
+Release Notes
+=============
 
-.. include:: release-notes-latest.rst
\ No newline at end of file
+.. include:: release-notes-latest.rst