stratigraphr 0.3.0

• Expanded framework for tidy radiocarbon analysis, adding:
  • New S3 object cal, a generic representation of calibrated probability distributions
  • Methods for printing and summarising cal objects
  • Type conversion functions for cal objects (as_cal.CalDates(), as_cal.oxcAARCalibratedDatesList() and as_cal.BchronCalibratedDates())
  • New vignette("tidy_radiocarbon")
• Breaking change: cal() and sum() renamed c14_calibrate and c14_sum and now return cal objects.
• Breaking changes to stratigraph interface:
  • Renamed functions: harris() → strat_connect(), is_valid_harris() → strat_is_valid()
  • Removed the notion of a "type" of stratigraph().
  • stratigraph() will now return a graph even if it is not stratigraphically valid.
  • Renamed vignette("harris") → vignette("stratigraph")
• Expanded the stratigraph interface, adding:
  • Utility functions for validating stratigraphies: strat_is_mirror()
• Fixed read_lst() when reading Stratify 'extended' LST files
• Added a NEWS.md file to track changes to the package.