[ccan] Changing from Public Domain to CC0

[Rusty Russell]

Damn lawyers!

Since Public Domain is a slippery concept outside certain countries, it
has been suggested that I formalize it to Creative Commons Zero.

I want to change the License string (and add a symlink) to the following
trivial modules.  Please Ack.

alignof
array_size
build_assert
check_type
compiler
container_of
err
hash
isaac
noerr
short_types
str
strmap
strset
tcon

Thanks,
Rusty.