Add new ellipse functions, peng data, fix problems

Version 1.6.2 (2024-02-14)

• Add peng dataset, a version of palmerpenguins::penguins
• Correct documentation problems from Roxygen 7.3.1 (@doctype)

Version 1.6.1 (2023-12-05)

• add warning to label.ellipse() if length(label.pos) > 1
• fixed label.pos in coefplot.mlm()
• add ellipse.axes() to draw axes of a covariance ellipse
• add ellipse.box() to draw conjugate axes of a covariance ellipse