Changes in Version 1.1

Calls to ppmlasso, env.var, ppmdat and sample.quad now allow for categorical variables. A binary column is
created for each unique factor of a categorical variable.

Added block cross-validation as a way to choose the LASSO or elastic net penalty in a call to ppmlasso.

The function ppm.dat from Version 1.0 has been renamed ppmdat to retain functionality with spatstat.

Fixed bug with sample.quad function so quadrature points no longer need to include the origin.

Fixed bug with predict.ppmlasso function such that point interactions may be included for area-interaction models.
