Add named vector and point quantities.
Merge branch 'master' into named-vectors-and-points
Spacetime points, Velocities.
lint
aoseuaeu
aoeuaoeu
Dates.
also the implementation.
After pleroy's review.
Merge pull request #147 from eggrobin/named-vectors-and-points

Named vectors and points
Merge remote-tracking branch 'la-vache/master' into the-return-of-the-plugin