Add ability to support soft scroll

[vkravets]

Soft scroll it's ability to scroll using pixel line not, text line....

It will be great:

1. Via config or via keyboard (??? Fantastic) turn on or turn off normal/soft scroll
2. Configure number of pixel line per one scroll.
3. Configure accelerator for above configuration for more speed smoother scroll.

For example you can see DOS text viewer with such functionality - http://www.oocities.org/siliconvalley/sector/5552/vs_down.htm

[vkravets]

Could you please point me where I can implement such logic? Because after splitting the code to different libraries is not clear for me where the render part and where functional and core part available in the code ((