Update echo example to support both plaintext and encrypted mode
Update echo example to support both plaintext and encrypted mode

wechatpy/wechatpy,cloverstd/wechatpy,cloverstd/wechatpy,zhaoqz/wechatpy,zaihui/wechatpy,jxtech/wechatpy,zhaoqz/wechatpy,zaihui/wechatpy,hunter007/wechatpy,messense/wechatpy,hunter007/wechatpy