Changed switch type to switch reflection and add doc for new SendString func
Changed switch type to switch reflection and add doc for new SendString func

vicanso/gorequest,fromkeith/gorequest,rockneurotiko/gorequest,roth1002/gorequest,jqs7/gorequest,QuentinPerez/gorequest,kemadz/gorequest,going/requests,julianshen/gorequest,csrgxtu/gorequest,parnurzeal/gorequest