dev-libs/stb: new package

dev-libs/stb: new package

This is a header-only package that curaengine uses. Curaengine tries to pull it
from git if not found on the system, which causes the build to break. This
package installs the header files in a place where cmake will find it during
the build.

Closes: https://bugs.gentoo.org/show_bug.cgi?id=670638
Closes: https://bugs.gentoo.org/show_bug.cgi?id=670604
Closes: https://bugs.gentoo.org/show_bug.cgi?id=670418
Closes: https://bugs.gentoo.org/show_bug.cgi?id=661416

Signed-off-by: Mathy Vanvoorden <mathy@vanvoorden.be>
Signed-off-by: Amy Liffey <amynka@gentoo.org>
Package-Manager: Portage[mgorny]-2.3.51.1