refine urllib code

- Update the npm test command
- Remove the unused code
- Fix the debug message
Simply the HTTPClient implementation
Merge pull request #41 from JacksonTian/refine

refine urllib code
Merge pull request #42 from JacksonTian/refine_httpclient

Simply the HTTPClient implementation
fix abort test
change test case
add args.contentType option
add contentType document
Release 2.0.1