robust: new package

Crate required by rnote #119 for robust predicates for computational geometry.

This depends on float-extras which is merged but not uploaded yet, to test this, build float-extras and ( cd build && ./build.sh robust librust-float-extras*.deb ). I patched out ieee754 and a feature depends on it which isn't useful for us, apart from that it's fairly standard.

Signed-off-by: Yifei Zhan debian@zhan.science