lock into pry v0.9.x releases

Pry v0.10.x has dropped support for 1.8.7.  This prevents bringing
in that dependency and breaking 1.8.7 compatible gems.
Merge pull request #9 from redding/kr-pry

lock into pry v0.9.x releases
generate/require a test support factory

This switches to require a modern assert version that provides factory
logic.  This then auto-generates and requires in a top-level `Factory`
implmentation that extends assert's factory.

This means all generated gems will have factory logic available by
default.