Add http copy module

This module can copy realtime http requests to specified destination, and orignal request will not be affected. 
With this module, we can copy online traffic to anywhere for testing or analysis.

Details:
- source: src/http/modules/ngx_http_copy_module.c
- test case: tests/nginx-tests/cases/copy.t
- documents:
 - [ngx_http_copy_module.md](https://github.com/chobits/tengine/blob/http_copy/docs/modules/ngx_http_copy_module.md)
 - [ngx_http_copy_module_cn.md](https://github.com/chobits/tengine/blob/http_copy/docs/modules/ngx_http_copy_module_cn.md)