Write guide on how Data Package compares with CSVW

[peterdesmet]

In response to #984, this PR adds a guide comparing Data Package with CSV on the Web (CSVW) a set of recommendations published by W3C in 2016 for documenting and accessing CSV files: https://www.w3.org/TR/2016/NOTE-tabular-data-primer-20160225/

It compares the two standards in terms of scope, maintenance, adoption (pending), building on other standards as well as a comparison of all CSVW properties and their equivalent in Data Package.