Add required attribute option to has_many associations
Allow required/scoped fields for belongs_to

In the process of adding this feature, I discovered a few bugs and
incorrect specs. When reading an attribute that was aliased,
it would never find it on the attribute hash because the attribute
is an alias. In the event that it can't read it from the attribute hash,
I will send it as a last ditch effort.

Also, a few associations were being incorrectly tested, so I modified
the tests.
Passing specs for .has_one with required attr
Removed aliased foreign key in post
Reove alias attributes and required field option

We decided that we just support the option for scoped attributes since
require was too generic. Also, alias attributes for foriegn keys weren't
great examples, so we just added new attributes.
Verify scoped attribute on object before assocation
Refactor  specs and implementation
Remove dependency to ffi-rzmq
refactor has_one assocation and specs
Check for guid before has_one association
check for nil before assocations
Merge pull request #14 from nelsonwittwer/nw/associations

Required or Scoped Attributes in Associations