Computes goodness of fit for regression model given vector of target and output values.
USAGE:
[gf] = gfit(t,y)
[gf] = gfit(t,y,gFitMeasure)

INPUT
t: vector of target values for regression model

y: vector of output from regression model.

gFitMeasure: string value representing different form of goodness of fit measure (for eg. '1' - mean squarred error, '5' - mean absolute error)

OUTPUT:
gf: goodness of fit values between model output and target