initial spike for using model class to implement validate
train and validate updated
Merge branch 'master' of github.gamesys.co.uk:PMP/modelr

Conflicts:
	NAMESPACE
	R/class-model.R
	R/train.R
	R/validate.R
	man/train_.Rd
Merge branch 'master' of github.gamesys.co.uk:PMP/modelr
Merge branch 'master' of github.gamesys.co.uk:PMP/modelr
- select_col used instead of [[
- message used in train
- unmodel.default added
- slice added
bugfix
bugfix

Conflicts:
	R/as-data-frame.R
	R/modelling-frame-dplyr.R