v0.5.0

unpivotr 0.5.0

New features

• behead_if() is for tiered headers within the same row or column. It takes
  filter functions similarly to dplyr::filter() to decide which cells to
  treat as headers, and can be applied more than once to the same row or
  column of headers until every tier has been dealt with.
• merge_rows() and merge_cols() combines header text when it is split over
  multiple cells.

Other changes

• behead(), enhead(), partition() and rectify() give a more informative
  error message for non-distinct cells, for example when trying to pass cells
  from more than one sheet to these functions (@gregrs-uk, #15).