v8.0.0

#1206 stripe-python v8 release This release introduces StripeClient and a service-based call pattern. This new interface allows you to easily call Stripe APIs and has several benefits over the existing resource-based pattern:
- No global config: you can simultaneously use multiple clients with different configuration options (such as API keys)
- No static methods for easier mocking
For full migration instructions, please refer to the v8 migration guide.

"⚠️" symbol highlights breaking changes

⚠️ Changed
- ⚠️ Request options like api_key, stripe_account, stripe_version, and idempotency_key can no longer be passed in positionally on resource methods. Please pass these in as keyword arguments.
BEFORE
```
stripe.Customer.create(
  "sk_test_123",  # api key
  "KG5LxwFBepaKHyUD",  # idempotency key
  "2022-11-15",  # stripe version
  "acct_123",  # stripe account
)
```
AFTER
```
stripe.Customer.create(
  api_key="sk_test_123",
  idempotency_key="KG5LxwFBepaKHyUD",
  stripe_version="2022-11-15",
  stripe_account="acct_123",
)
```
- ⚠️ Methods that turn a response stream (Quote.pdf) now returns a single value of type StripeResponseStream instead of a tuple containing (StripeResponseStream, api_key).
- ⚠️ Removed public access to APIRequestor. APIRequestor's main use is internal, and we don't have a good understanding of its external use cases. We had to make several breaking changes to its interface as part of this update, so rather than leaving it public we made it private. If you have a use case for APIRequestor, please open up a Github issue describing it. We'd rather you rely on something specifically designed for your use case than having to reach into the library's internals.
⚠️ Removed
- ⚠️ Remove api_version from File.create parameters. Please use stripe_version instead.
- ⚠️ Remove util.read_special_variable() utility method (importing directly from stripe.util is deprecated as of v7.8.0)
- ⚠️ Remove StripeError.construct_error_object(). This method was intended for internal stripe-python use only.
- ⚠️ Remove ListObject.empty_list(). This method was intended for internal stripe-python use only.
- ⚠️ Remove SearchResultObject.empty_search_result(). This method was intended for internal stripe-python use only.
- ⚠️ Remove StripeObject.ReprJSONEncoder. This class was intended for internal stripe-python use only.
- ⚠️ Remove StripeObject.api_base. This property was defunct and returned None.

See the changelog for more details.

⚠️ Changed

⚠️ Removed