Second pre-release for v0.9

It's been almost 3 months since Zoph 0.9pre1 has been released, a lot longer than I anticipated but I have been busy...

Two bugs were found in Zoph 0.9pre1 and they have been fixed in this release. See the changelog for more details.

Anyone running v0.9pre2 is recommended to upgrade to this version. Please report any bugs you find, so I can fix them in the next release. To upgrade, please read the upgrade instructions.