pxmake 0.14.0

New features

• Prepare for CRAN submission. (#330)
• Add validate = option to all modifying functions to enable turning off
  validation. (#332)
• Add functions px_classification() and px_classification_save() to create
  and save classifications (value sets and aggregations). (#327)

Bug fixes and minor improvements

• px_elimination(), px_map(), and px_domain() now only sets value for
  STUB/HEADING variables if value is character. (#325)
• Optimize px_micro() by only setting stub once, instead of for all files.
• Add na_to_star option to px_cellnote() and px_cellnotex(). (#335)
• Support PX-files with cell values that contain closing parentheses. (#337)
• Avoid all R CMD Check notes, warning and errors.
• Add CRAN installation instruction.
• Use name 'PX-files' consistently.
• Update package title and description.
• Add examples and return for all exported functions.
• Reduce size of large files.