restore go1.13 availability

rename pointer.Get to pointer.ValueOf

add proxy call for errors

issue #45: rename io.Discard to io.Discarded and improve it for defer…

… call

fix #44: add testing.Content

fix #43: add io.Discard to works together with safe.Close and http.Re…

…sponse

fix #41: add experimental request builder

fix #42: add unsafe.Return function

issue #40: extend built-in sort package

refactor tests and remove gcflags