PolMine/cwbtools: Late Vintage

This is a minor release that anticipates an upcoming change in R's matrix class, that will inherit from the array class starting with R 4.0.

• The pkg_add_corpus() function will now create the cwb directories (registry and data directory) if necessary. Previously, these directories were required to exist before moving a corpus into a package, making it necessary to put dummy files into packages to keep R CMD build from issuing warnings and git from dropping these directories. Creating the directories on demand is a precondition for a CRAN release of data packages (#11).

• In the upcoming R version 4.0, the matrix class will inherit from class array. The new package version now takes into account that length(class(matrix(1:4,2,2))) will return the value 2.

• The NEWS file now follows the styleguide such that pkgdown::build_site() will generate a proper changelog page.