Removed code duplication (first_or_empty_if_nil).
sanity check configure exception in a separate method.
Merge branch 'master' of github.com:ncbo/goo
default values bypass min cardinality 1. Fixes #56.
Default naming policy forces to have exactly one :unique attribute.
Model.find fails if there are not any unique attributes (fixes #55)
Uri validator (close #58)