Support providing parameter values and post body values

[yxl]

The project is awesome! The pull request want to make the project more perfect by providing the following patches:

• getEndpointSnippets supports an optional values parameter to provide query parameters. However other 3 types of parameters, such as header, path and cookie are not supported. The pull request extends the values parameter to support other 3 types of parameters.
• Considering postBody is another commonly used way to pass parameters, the pull request support the set the postBody values as well.
• In addition, the pull request updates the test.js to cover the patches and all tests has been passed.