Vector spec v1.0-rc2

Krste Asanovic

I've finally finished an extensive pass over the whole spec, and
believe it should be ready for public review but given that it's late
on a Friday, I would like to give at least one more sleep cycle before

So, last call to make last-minute suggestions on this version I've
tagged as v1.0-rc2 before I pass final version to the team to release
tomorrow (that will be tagged v1.0).