Solid Path

• Package names, software names and API are wrapped in single quotes in the
  DESCRIPTION files, to follow section 1.1.1 of 'Writing R extensions' #43.
• References in the description of the DESCRIPTION file have been standardized
  #44.
• To meet CRAN requirements, any remaining usage of install.packages() has
  been removed from the package. Using argument pkg of corpus_install() will
  install corpora found in a package as system corpora defined in the default
  registry directory #46.
• The vignettes 'opennnlp.Rmd' and 'sentences.Rmd' have been removed from the
  package; they are now part of the PolMine Cookbook repository at
  https://github.com/PolMine/cookbook. Packages 'NLP' and 'openNLP' are no
  longer suggested and the install.packages() call (though not evaluated) is
  omitted. Part of the fix for #46.
• The fs::path() function replaces base R file.path() throughout to solidify
  the generation of paths and to improve the readability of the code throughout.
• p_attribute_encode() checks that the character vector token_stream does
  not exceed the CWB corpus size limit (2^31 - 1) #40.