5.21.2 release

1. Add spot cross margin API support
2. Add spot order operations using cross margin account
3. Withdrawal supports cancelling
4. Futures positions supports updating cross margin leverage
5. Add interest in spot margin account response

5.15.3 Release

1. Add GateApiException. Refer to API documents for details
2. Remove redundant code
3. Add missing fields in Contract model

5.15.2 release

5.15.2 supports all new APIs since 4.14.0, along with some breaking changes:

1. Drop support for PHP<7.1
2. Optional parameter passing are changed from one by one to associative array so that you can leave them to default
3. The authentication has been rewritten, For how to initialize a client, refer to the API documentation.