#270 - Return a query builder for has many associations instead of array

[webandtech]

This PR addresses issue #270 which is that has_many associations only return an array, not a query builder which can accept params for querying the relationship.

This does not change the behavior of has_one or belongs_to associations.

With this PR, the has_many association no longer executes the query immediately instead, it returns a query builder based on the association class that you may use to query the association, such as by calling '#all' to get a paginatable ResultSet or applying other params to the query.

Owner.properties
#=> #<JsonApi::Query::Builder:0x007fca7197e350...>
props = Owner.properties.all
#=> [#<Property:@attributes=...,#<Property:@attributes=...]
props.next_page
#=> [#<Property:@attributes=...,#<Property:@attributes=...]

[webandtech]

@jamesotron @chingor13 I know this changes the behavior significantly but seems like the best way to adhere to the spec and provide a full query interface such as the ability to apply params to the association query such as Owner.properties.select('name').all.

To maintain backward compatibility we could possibly introduce a configuration option to return the query builder and change the default functionality to return a paginatable ResultSet. Looking forward to your thoughts!

[jsmestad]

@webandtech this is great! I pulled it into my fork along with a handful of the other outstanding PRs on this project jsonapi-consumer