Calculate P values from the F distribution, corresponding to specified F
statistic and degrees of fredom. Also calculates critical values for the same F
distribution corresponding to the specified alpha (significance) level.

Inputs are the test statistic, degrees of freedom for the numerator and
denominator of the F statistic and the specified alpha for calculation of critical values.

The program outputs the P value corresponding to the given inputs, the critical value
corresponding to the given alpha and the probabilities associated with values greater than or less than the observed F value,
as well as a summary and plot of the distribution.