New features

New param in plotRSA: suppress.grid.
If link="probit" in plotRSA, the 3d plot automatically scales the z-axis to c(0, 1)
If link="probit" in plotRSA, the raw data points now can take the predicted probability (plotRSA(..., points=list(value="predicted")))
cex params in plotRSA slightly changed: now we have three cex parameters to independently control the font size of the main title (cex.main), the axes labels (cex.axesLabel), and the tick labels (cex.tickLabel)
New surface parameter for testing strict congruence patterns ("a5"). Thanks to Sarah Humberg for implementation.

Bug fixes

Fixed a wrong formula in the standard error of a4 (the formula was corrected in an erratum of Shanock, L. R., Baran, B. E., Gentry, W. A., & Pattison, S. C. (2014). Erratum to: Polynomial regression with response surface analysis: A powerful approach for examining moderation and overcoming limitations of difference scores. Journal of Business and Psychology, 29, 161. http://doi.org/10.1007/s10869-013-9317-6. Thanks to Sarah Humberg for pointing to the erratum).
Fixed a bug in the curvature of the principal axes (closing issue 2 on Github; thanks to scith for reporting the bug).