Robust PCA by Projection Pursuit

 Provides functions for robust PCA by projection pursuit. The methods are
 described in Croux et al. (2006) <doi:10.2139/ssrn.968376>, Croux et al.
 (2013) <doi:10.1080/00401706.2012.727746>, Todorov and Filzmoser (2013)
 <doi:10.1007/978-3-642-33042-1_31>.