Added error formating.

[jerel]

By default validation errors will be formatted like so:

{
    errors: [{
        detail: 'First name is required',
        source: {
            pointer: '/data/attributes/first-name'
        },
        status: '400'
    }]
}

However if you want to throw a custom validation error you can pass a dictionary and it will be used:

def validate_first_name(self, data):
    raise ValidationError({ 'detail': 'Gimme your first name' })

results in

{
    errors: [{
        detail: 'First name is required'
    }]
}