I noticed that none of the other third-party extensions had a `config.hdf` file in their repository. Were you executing HHVM with this config file by specifying its path on the command line? I think documenting that the user should add the extension to their own config in the README is more flexible, since users might already have a real configuration with more options than our extension.

@sgolemon: What's the difference between `example = /path/to/extension.so` and `* = extension.so` with a DynamicExtensionPath set (as in the [pgsql](https://github.com/PocketRent/hhvm-pgsql#building--installation) driver)?