use importlib to find data files

[pkienzle]

For example, replace:

periodictable/periodictable/activation.py

Lines 914 to 915 in 0b8ba54

	path = os.path.join(core.get_data_path('.'), 'activation.dat')
	with open(path, 'r') as fd:

with:

import importlib.resources as res
with res.open_text("periodictable",  "activation.dat") as fd:
    ...

[pkienzle]

Instead of having the datafiles in the package, put them in the explore directory and use them to generate preparsed data for the package. If the data is converted to python structures inside python modules then there will not be any need for shipping datafiles as resources.