Add service method to delete/reset all contexts.

[coreyroach]

I have added a prototype function to the apiai service module to delete/reset all active contexts. The update modifies the ContextsRequest object to accept a method option to pass DELETE as the method. This will default to POST if no method option is given. The end method also checks if the request method is POST before writing the body content.

The new method is named deleteContextsForSession and I have included an example.

[sstepashka]

This feature is useful, but... May we create new request class for delete contexts for splitting code and do its more clearly? This will simple code. Also, please, if you can, add type definition about this method to TS definition file (index.d.ts)?

[coreyroach]

Would this new class (call it DeleteContextsRequest) extend ContextsRequest or extend JSONApiRequest?

[sstepashka]

I think, use JSONApiRequest. just constructor with parameters with sessionId and override one method to provide DELETE http method.

[coreyroach]

I have created a new request class and reverted the ContextsRequest class. Also, I have updated the example and TS definition.

[sstepashka]

Thank you!