CCAN 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
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.