PolMine/cwbtools: Apple Picker

NEW FEATURES

• The corpus_install() gives much better and nicer reports on steps performed during corpus downloads. User dialogues have been reworked thoroughly to provide better user guidance.
• The use_corpus_registry_envvar() function is called by corpus_install() and will amend the .Renviron file as appropriate if the user so desires.
• To resolve a DOI, the 'zen4R' package is used, to extract information on the whereabouts of a corpus tarball efficiently from the Zenodo API.
• A corpus_testload() has been implemented to check whether a (newly installed) corpus is accessible.

• Extracting the version number from the corpus tarball is somewhat more forgiving if the version number does not start with "v".
• The registry file for a newly downloaded corpus is refreshed only if a temporary registry directory is used.
• To remedy the fairly common error that the path to the info file is not stated correctly in the registry file, a fallback mechanism will look up potential alternatives to an info file stated wrongly.

• The json string returned from Zenodo may include newline strings that are escaped such that they cannot be processed by jsonlite::fromJSON(). The auxiliary function to get and process information from Zenodo now ensures that newline characters are escaped such that they can be processed.
• The corpus_copy() function did not set the path to the info file to the new data directory - corrected.
• The corpus_install() function failed when the registry_dir got a NULL value from the default call to cwbtools::cwb_registry_dir(). But if the directories are created, the registry directory is there. Fixed.
• Removed a bug (faulty assignment) that would prevent that the path of a registry file is handled correctly (i.e. wrapped in quotation marks) by registry_file_compose() when the path includes any whitespace characters.

• A problem with updating the curl dependency of cwbtools that may arise when devtools::install_github() is used is addressed in an extended explanation in the README.md file how to install the development version of cwbtools using remotes::install_github() (#21).