Removed import_annotations_table, added VariantDataset.from_keytable

We’ve removed the import_annotations_table module, but it’s still possible to create a VDS from a text file using a new function VariantDataset.from_keytable:

>>> vds = VariantDataset.from_keytable(kt.key_by('Variant'))

The keys options has also been removed from HailContext.import_keytable – use key_by after the import:

>>> hc.import_keytable('my_table.tsv').key_by('KEY_COLUMN')