Previous Sputnik integration caused API change: Vocab, Tagger, etc
were loaded via a from_package classmethod, that required a
sputnik.Package instance. This forced users to first create a
sputnik.Sputnik() instance, in order to acquire a Package via
sp.pool().
Instead I've created a small file-system shim, util.Package, which
allows classes to have a .load() classmethod, that accepts either
util.Package objects, or strings. We can later gut the internals
of this and make it a proxy for Sputnik if we need more functionality
that should live in the Sputnik library.
Sputnik is now only used to download and install the data, in
spacy.en.download
