v1.1 - MonotonicOptimalBinning

In version v1.1, we added the new feature sign which will allow the program to determine the default direction in the given independent variable.

In general, we can now pass our judgment whether the relation between x and y is +(positive) or -(negative), or just passing auto to let the program decide by the Pearson correlation.

There are three arguments that can be passed into init_sign argument:

1. auto : Program will calculate the Pearson correlation between the x and y and decide the direction.
2. + : Manually given this sign means that the user assumes greater the x is, higher mean of y.
3. -: Opposite of giving +.