Provide option for input scaling as a vector #291
Description
In A Practical Guide to Applying Echo State Networks the author suggests to scale the columns of the input matrix individually. At the moment this option is not available, but it could be useful to introduce.
The idea would be that the keyword scaling can be either a number or an array. In the case it's an array then each column is scaled according to the values of that array i.e. scaling = [(-0.1, 0.1), (-0.3, 0.3)]. At the same time we could also relax the scaling itself, making it easier to control the bounds of the distribution