fix api of and mark region config is optional (ucloud#11)

BUGFIX:

- Mark `region` config is optional
- Update field `CPUSet` at the model `PHostSetSchema`

migrate from python3 (ucloud#10)

FEATURE:

- Add `SendUSMSMessage` as public api
- Add `GetUSMSSendReceipt` as public api
- Add `CreateUSMSSignature` as public api
- Add `QueryUSMSSignature` as public api
- Add `UpdateUSMSSignature` as public api
- Add `DeleteUSMSSignature` as public api
- Add `CreateUSMSTemplate` as public api
- Add `QueryUSMSTemplate` as public api
- Add `UpdateUSMSTemplate` as public api
- Add `DeleteUSMSTemplate` as public api

fix utf8 header in documentation (ucloud#8)

add stepflow sdk (ucloud#5)

FEATURE:

- Add the SDK of `StepFlow` product (ucloud#5)

BUGFIX:

- Fix the `NoneType` error for `RetCodeException` (ucloud#5)

Feature/typesystem enhancement (ucloud#4)

* migrate from python3 sdk

* migrate from python3 sdk

improve docs & fix user agent (ucloud#3)

ENHANCEMENT:

- Improve documentation: add response fields and models to service documentation (ucloud#3)

BUGFIX:

- Fix transport keywork arguments has no-effected error, add user-agent to default headers (ucloud#3)

fix sucure token (ucloud#2)