Enhance Py_ARRAY_LENGTH(): fail at build time if the argument is not an array

Move other various macros to pymcacro.h

Thanks Rusty Russell for having written these amazing C macros!
diff --git a/Misc/ACKS b/Misc/ACKS
index 0d1a77b..06feb0b 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -825,6 +825,7 @@
 Jeff Rush
 Sam Rushing
 Mark Russell
+Rusty Russell
 Nick Russo
 Patrick Sabin
 Sébastien Sablé