fix: calculate accurate body size when posting files (#42)

fix: set body back after io.Copy it to buffer (#38)

feat: add Dump option for easy debugging (#26)

* feat: add Dump option for easy debugging

* feat: add dump example to README.md

feat: add ToText and ToJSON options for easy use (#24)

* feat: add ToText and ToJSON options for easy use

* docs: update README

* test: add unittest about JSON post

* fix: update README.md

feat: set some types to internal (#21)

feat: attach error with http body text

feat: return response body as bytes (#13)

Co-authored-by: youngerli <youngerli@tencent.com>

fix: return error if response is nil

feat: disable keep alives (#10)

Co-authored-by: youngerli <youngerli@tencent.com>

feat: combine options (#9)

Co-authored-by: youngerli <youngerli@tencent.com>