GNU R tidying methods for mixed models

 Convert fitted objects from various R mixed-model packages into tidy
 data frames along the lines of the 'broom' package. The package provides
 three S3 generics for each model: tidy(), which summarizes a model's
 statistical findings such as coefficients of a regression; augment(),
 which adds columns to the original data such as predictions, residuals
 and cluster assignments; and glance(), which provides a one-row summary
 of model-level statistics.