Use "coordinate variables"/"data variables" instead of "coordinates"/"variables"?

[shoyer]

Recently, we introduced a distinction between "coordinates" and "variables" (see #197).

CF conventions make an analogous distinction between "coordinate variables" and "data variables":
http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html

Would it be less confusing to use the CF terminology? I am leaning toward making this shift, because netCDF already has defined the term "variable", and xray's code still uses that internally. From a practical perspective, this would mean renaming Dataset.vars to Dataset.data_vars.

CC @akleeman @ToddSmall