This PR moves the io.py file into dlg.data.
As a side-effect, to avoid circular imports, the data drops have been nested into a dlg.data.drops sub-module.
Coverage decreased (-0.01%) to 82.126% when pulling 3086f4acaad0a21ff3474a68df81bfc949283925 on move-io into 1cd863cc29124cd5466b2a47571adc63a9a95319 on master.
This PR moves the io.py file into dlg.data. As a side-effect, to avoid circular imports, the data drops have been nested into a dlg.data.drops sub-module.