Move _snappy out of global namespace

During the package review for fedora, the reviewer spotted that `_snappy` is in the global namespace. Since it is private it may be a good idea to move it in its own namespace. See https://bugzilla.redhat.com/show_bug.cgi?id=1244514#c10

Start by locating the `_snappy` binding and checking how it is exposed from the package. Read the Fedora review discussion linked in the issue for the namespace requirement. Done means the private binding is no longer placed in the global namespace without breaking the package interface.

索引モデルが issue の本文から書いたものです。