#238 Smoothing line

[Pere Pujal i Carabantes]

Something in the line of Inkscape's "Draw freehand lines" when setting "Smoothing " to 20 or so to smooth pointer irregularities.

Could be implemented as a magic tool, single sizeable brush or as a paint mode, harder, more brushes, but non-contiguous brushes will not benefit from it.

[William Kendrick]

I got something going (work-in-progress). Check for magic/src/WIP/smooth.c coming to master soon. Once 0.9.30 is out the door, I'll move it up a directory so we can include it in 0.9.31.

I just lifted the Bezier curve code from calligraphy.c and repurposed it. :)