Log Message:
py-cffi: updated to 1.13.1

v1.13.1
* deprecate the way to declare in cdef() a global variable with only void *foo;. \ 
You should always use a storage class, like extern void *foo; or maybe static \ 
void *foo;. These are all equivalent for the purposes of cdef(), but the reason \ 
for deprecating the bare version is that (as far as I know) it would always be \ 
mistake in a real C header.
* fix the regression RuntimeError: found a situation in which we try to build a \ 
type recursively.
* fixed issue 427 where a multithreading mistake in the embedding logic \ 
initialization code would cause deadlocks on CPython 3.7.