Fix lookup loading

[thatbudakguy]

The way lookups are loaded now doesn't seem to be right. The files themselves are available in tests:

spacy-och/tests/test_lookups.py

Lines 12 to 14 in 3746a19

	py_lookup_path = spacy.registry.lookups.get("och")()["pinyin"]
	pinyin = srsly.read_json(py_lookup_path)
	self.assertEqual(pinyin["㐁"], ["tiàn"])

But what we really want is for the table to be preloaded and available at nlp.vocab.lookups. Maybe this will require setting up an entry point for the lookups.