Nix / Guix compatibility

[f9cef2aa at yandex.ru]

>CFFI fails to find libraries on Nix / Guix.  This is (probably) because those two
>distributions don't follow the traditional filesystem hierarchy /lib,
>/usr/lib, etc.
>
>For instance, trying to load sqlite-lib yields the following backtrace:

Nix doesn't give you a global sqlite3 version anyway…

You can change $LD_LIBRARY_PATH or change CFFI's library search path to
point to the version from Nixpkgs channel or checkout you prefer.