Added floppy icon ( Save )

[psjishnu]

Added save icon ( floppy-fill )

Fixed Issue #272

[psjishnu]

[psjishnu]

Please mention how to update bootstrap-icons.svg file

[MrKuzio]

Hey, @psjishnu would you be able to review the shape of the icon?
It seems a bit too different from the shape of an actual floppy disc.

Also, I think another point of improvement would be to increase the thickness of the stroke on smaller sizes. SO the lines would still be visible.
It would be great if you could specify the size in pixel and to make it never smaller than 1px, and try to avoid as much as possible to make the stroke size become portions of pixels. This to avoid pixelation.