fix tests from last time (boolean coercing, uinteger default to 0)
clarify difference between uuid v4 and non-v4, add test, `id` schema type is now just checking for ObjectId
rename mixin to mixins
Merge pull request #6 from airbrite/peter/uuid

Clarify uuid v4 vs non-v4 and `id` schema type is now just checking for ObjectId