powerjoin 0.1.0

• The join functions will fail if not provided a check argument built with check_specs()
• New functions paste_xy() and paste_yx() to conflict columns by pasting, ignoring NAs and empty strings by default
• using rw ~ ... in the conflict argument is better documented
• The class of dates is not lost anymore when using rw ~ ... in the conflict argument
• Obsolete imports were removed
• Rebuilding the documentation solves the issues that got the package kicked from CRAN