It reads the population projections by age, sex and education
of the Wittgenstein Centre Human Capital Data Explorer as downloaded by
downloadWCDE(). The output format follows readLutz2014():
a magpie object with the dimensions country, year, scenario, sex, age and
education in million people. In addition to the education categories of
Lutz2014, the datasets contain a finer split of the highest levels
("Short Post Secondary", "Bachelor" and "Master and higher"). These belong
to a separate classification level and do not sum to "Post Secondary".
Age-education combinations that do not occur (e.g. a young child with a
university degree) are set to 0, as in Lutz2014. Country-year slices that are
entirely absent from the source (the pre-2015 reconstruction is missing for
some countries in "epop_v2") are kept as NA. World and continental aggregates
(UN M49 codes >= 900) are removed.