Adding class objects to model the DET curves

Override standard

`plot()`

function when called with a*DET*or*DETs*objectRenaming function

`printDET()`

to`show()`

.New functions to compute performance measures:

`EER()`

and`mindDcf()`

.New functions to cplot the correspondent ROC curve from a DET curve:

`plotROC`

and`plotROCs`

.

`printDET()`

shows the names of the classifiers to access de DET object.`detc()`

and`detc.CI()`

do not plot the EER. How to to that is described at the example`speaker`

and`ovarianCancer`

databases are added for complementing real examples of using DET curves.

New function

`printDET()`

for describing the DET returned parameters.`det()`

and`det.CI()`

are renamed as`detc()`

and`detc.CI()`

to avoid overriding.New

`detc()`

and`detc.CI()`

functions now provide an estimation for the Equal Error Rate (new field at the returned dataframe)

New aspect of ROC Curve plot.

`det()`

and`det.CI()`

now inlcude*xlim*and*ylim*arguments to select the axes limit of the plot.