Add features

Version 0.6.2

This is a modest upgrade to the initial release, adding a number of features.

• corrected small bugs in ggbiplot() and ggscreeplot()`
• reflect() now also reflects supplementary variables from FactoMineR::PCA()
• added support for ade4::dudi.pca()
• ggbiplot() gains an axis.title argument
• ggscreeplot() gains color, shape, linetype and linewidth arguments
• Added get_SVD() intended the simplify the interface to various PCA functions.
• Now use get_SVD() in ggbiplot() and ggscreeplot()
• Extend some examples, requiring Depends:ggplot2