DOC: change doc refs to 0.13.1
@jtratner @y-p  ok?

don't need to change setup? (its set at 0.13.0 until next release, right?)
 Changes look ok to me.
Don't know about setup.py, that's up to you and @jtratner.
 will just leave the version nums as is for now (and they make sense now that 0.13.1 is (maybe) the target)..

if we decide to switch to 0.14 then it won't matter anyhow as it will be reset for 0.14
