We need this commit:

    http://git.ozlabs.org/?p=ccan;a=commitdiff;h=c38e11b508e52fb2921e67d1123b05d9bef90fd2

or else we segfault on really big arrays allocation instead of getting
ENOMEM and reporting it as MemoryError to python.

Unfortunately in CCAN they made separation of list_head into list_head &
list_node (for better type safety I suppose), but that leads e.g. to
inablility to insert element in the middle of the list.

We take the code from util-linux.git (v2.25-165-g9138d6f)[1] which claims
LGPL license for it, with which we are fine.

[1] https://git.kernel.org/cgit/utils/util-linux/util-linux.git/tree/include/list.h?id=v2.25-165-g9138d6f

CCAN[1] is a "Comprehensive C Archive Network" - a collection of useful
C libraries to use.

Wendelin.core will be a C project in big part, so having CCAN at hand is
useful.

We hook CCAN as git submodule, without copying it into git repo. Later
on making source tarball distribution, the code will be injected into
generated tarball, so there will be no additional dependencies to
download something from network for end users.

[1] http://ccodearchive.net/