alias dev-master to 1.3.x-dev

I think that's what it really is for the moment: the next 1.3.x
(development version). Aliasing this branch to 1.3.x-dev allows people
to install dev-master but keep a real version constraint (like ~1.3) and
be confident they're not going to get BC-breaks.
Merge pull request #120 from greg0ire/alias_master_branch

alias dev-master to 1.3.x-dev