Raise errors for invalid blueprints for associations

[caws]

This PR validates that a given Blueprint class passed for an association is valid and inherits from Blueprinter::Base.

The issue.

Take the following Blueprinter.

class PaymentBlueprinter < Blueprinter::Base
    identifier :id
    view :estimate do
      association :client_taxes, blueprint: Client, view: :estimate
     # or 
     # association :client_taxes, blueprint: {}, view: :estimate
    end
end

This raises undefined method `prepare' for #<Class:0x00005649611cdb70> Did you mean? prepend when this line is interpreted.

The fix:

Add logic to raise errors if Blueprinter::Base is not present in the ancestor list of the class provided as the Blueprinter for a given association.

My thoughts:

The undefined method error is not intuitive and does offer any hint as to what's going on to the programmer. As an extra I also added a check to see if the provided Blueprint class has any ancestors at all.

[philipqnguyen]

Great idea, I have a suggestion.