0.99.17.1

• Added syntactical sugar to manipulate annotations and attributes.
• Fixed import of value labels for string variables in 'spss.system.file'
• Fixed codebook representation of datetime items in SPSS system and portable files
• Support for date or datetime import added to 'spss.portable.file'
• Support for date or datetime import added to 'spss.system.file'
• Minor bugfix in printing of 'datetime.item's - added bracket method for
  this class of objects
• Fixed issues flagged by Tomas Kalibera's rchk utility