Secret Spell

• New function p_attribute_rename(), corresponding to s_attribute_rename().
• p_attribute_encode() will remove the [p_attr].corpus file as suggested by
  cwb-makeall (if compress is TRUE).
• Assumptions about the statement of an info file in registry files are relaxed,
  the line starting with "INFO" is not required.
• Internally, functionality from the fs package for a consistent handling of
  paths (such as fs::path()) is used more widely (#36).
• Assumptions about the definition of a version in the name of a corpus tarball
  are relaxed. If possible, the version is taken from the properties (i.e. the
  registry file).
• New function zenodo_get_tarball() for downloading corpus tarballs from
  Zenodo. Restricted access can be handled too (personalized URL with token).
• Function corpus_install() has new argument load to control whether corpus
  is loaded after installation.