Notable changes included in v4

Breaking changes

idempotency package has moved from the mollie directory to the pkg directory.
pagination package has moved from themollie directory to the pkg directory.
connect package has moved from the mollie directory to the pkg directory.
root namespace is not github.com/VictorAvelar/mollie-api-go/v4/.
Changes in all resources:
- Data structures to describe request content in create, update and get operations are no longer the same, e.g. for payments there is a CreatePayment struct, a UpdatePayment struct and a Payment struct. This enables future extensions and modifications without having to check for cross request compatibility.
- Data structures that describe available url parameters are consistently names List{ResourceName}Options.
- Data structures that describe lists responses are consistently named as follows: e.g. for payments: PaymentsList
API aliases now use the parent objects, e.g. for settlements when listing payments the options passed to the request are using the ListPaymentsOptions object and not a local object.
All resources were checked for API consistency and parity, optional resources with custom types are now pointers to ensure proper json encoding and decoding to avoid issues as the one mentioned un #271
All resources embed a struct containing all the fields specific to access tokens, following this pattern the same happens for fields specific to Mollie connect