Yscope

adresses #446 (closed)

Adds yscope keyword to plot functionality:

since i guess, rightfully so, it will be questioned that yscope does not just be processed in parallel to xscope:

• when one would just cut off the data exsessing y bounds and than plot it as done with xscope, you would plot connecting lines between points, that are actually seperated by points not in the viewing range.
• while for the x-axis limits it is only natural to have all series in one plot displayed with the same x range, that is not true for the y-axis. So in analogy to the label keywords, yscope can also be a list or dictionary that applies different limits to the variables displayed.