Define direction of sampling in the Sampler-module

[SMEISEN]

What is your feature request related to?

• Problem related

Please describe the module/problem

Currently, the Sampler samples the data in backwarding direction:

data = [1,2,3,4,5]
Sampler(3)
===========================================
[1,0,0]; [2,1,0]; [3,2,1], [4,3,2], [5,4,3]

Describe the solution you'd like
Allow sampling in forwarding direction

data = [1,2,3,4,5]
Sampler(-3)
===========================================
[0,0,1]; [0,1,2]; [1,2,3], [2,3,4], [3,4,5]

[SMEISEN]

Maybe change the syntax of sample_size

positive for sampling in forwarding direction
negative for sampling in backwarding

Implement FutureWarning?