1.7 branch creation

[Josh Elser]

End of week? Any objections/complaints/opinions/cat-pictures?
I'm thinking our branches would then look like

1.5 -> 1.5.3-SNAPSHOT
1.6 -> 1.6.3-SNAPSHOT
1.7 -> 1.7.0-SNAPSHOT
master -> 1.8.0-SNAPSHOT

I think we still want to hold off on 2.0.0 because it's too amorphous 
right now and w/o any concrete code ready to go into such a branch.

- Josh