consistency in idTypes

[ericblade]

[ericblade]

we also have similar in condition

type MWSItemCondition =
    | 'New'
    | 'Used'
    | 'Collectible'
    | 'Refurbished'
    | 'Club';

type AdvItemCondition =
    | 'used'
    | 'new'
    | 'collectible'
    | 'refurbished'
    | 'club';

I'm pretty sure we are converting it to lowercase intentionally, and also that some Amazon APIs are inconsistent in their usage. I think when I went through all the docs to write ts-amazon-mws, I was surprised at how inconsistent either their APIs or their documentation are.