cv.parameter.test: cross validation parameter test
In sbbrandt/xgbAnalysis: Reaction coordinates analysis

calculates cross validation for given parameter and a testparameter

1 2	cv.parameter.test(testpar, nfold, nthread, nrounds = 200, plot = T, pdim = 10, width = 1.5)

`testpar`	e.g. list(eta = 0.1, 0.2, ...)
`nfold`	how many folds of dataset
`nthread`	number of CPU cores to use, NA for all
`nrounds`	number of training rounds
`plot`	should results be plotted, default=TRUE
`pdim`	dimension of plot, default=10
`width`	proportion of width to height, default=1.5