graphics/mypaint-brushes: import mypaint-brushes-mypaint-brushes-1.3.0

Brushes used by MyPaint and other software using libmypaint.

This data package is versionned. This are the brushes to be used
by libmypaint 2.x, current development version which has no releases
to the day of writing. If you want brushes for the libmypaint 1.x
releases, do not install mypaint-brushes from master, but from
"v1.3.x" branch (or last release tagged with a "v1.x" version).

(ryoon)