Update mod.rs add handle the response type properly

[subhashdasyam]

Handle the response types

It only handles text/* and application/*

if application/octet-stream is present it downloads few bytes and check if the data is binary or readable text, if its readable text it responds as is, if its binary data it ignores.

if the content-type is image or so it ignore for now :)

@evilsocket basically handles #15