Prova v1.9.0

• The package does not require the package 'extraDistr' any longer.
• Internal changes to some functions.
• Improved and more consistent digit-rounding system for print() output of probabilities.
• Fixed some bugs in the use of Pr() with base-rate correction (non-null argument 'priorY').
• Changed the class of mutual information objects to "mi".
• Introduced a print() method for mutual-information objects.
• Improved print() display for probability and mutual-information objects.
• Improved plot.probability(); singular probability (e.g. at censored values) are now displayed on a separate scale.
• Changed the behaviour of the TRUE value of argument parallel =: now it queries the value of the user's option "cl.cores", via getOption(), or uses 2 if that value is NULL (this is the same behaviour as in R's documentation for the clusterApply functions).
• Updated documentation.
• Re-tested some functions.
• Cleaned some code.