Include structseq.h in Python.h, and remove now-redundant includes in individual sources.
diff --git a/Misc/NEWS b/Misc/NEWS
index f39b2e2..2eb41df 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -136,6 +136,8 @@
 C-API
 -----
 
+- structseq.h is now included in Python.h.
+
 - Loosen PyArg_ValidateKeywordArguments to allow dict subclasses.
 
 Tests