Postgres 9.4 hstore supports types

[drbawb]

hstore is used for the attributes bundles, which store metadata that is used to organize collections of related torrents.

Currently hstore only supports text which means babou is responsible for serializing its data to-and-from strings; which is both expensive and fragile.

postgres 9.4 adds support for types to hstore documents so I may require a minimum version of PostgreSQL 9.4 to leverage this.