doc and api tweaks for producer
doc and api tweaks for producer

raisemarketplace/sarama,crast/sarama,vrischmann/sarama,gyroscope-innovations/legacy_sarama,DataDog/sarama,cep21/sarama,winlinvip/sarama,rafrombrc/sarama,VividCortex/sarama,pronix/sarama,yangfan876/sarama,uovobw/sarama,HelixEducation/sarama,Shopify/sarama,remerge/sarama,kraveio/sarama,DataDog/sarama,kmiku7/sarama,kraveio/sarama,VividCortex/sarama,HelixEducation/sarama,cep21/sarama,Neuw84/sarama,crast/sarama,aybabtme/sarama,jepst/sarama,LastManStanding/sarama,jepst/sarama,vrischmann/sarama,yangfan876/sarama,rafrombrc/sarama,betable/sarama,aybabtme/sarama,jimmykuo/sarama,sclasen/sarama,mailgun/sarama,scalingdata/sarama,jimmykuo/sarama,uovobw/sarama,mailgun/sarama,pronix/sarama,winlinvip/sarama,gyroscope-innovations/legacy_sarama,Neuw84/sarama,LastManStanding/sarama,xiaotianlis/sarama,betable/sarama,raisemarketplace/sarama,scalingdata/sarama,remerge/sarama,Shopify/sarama,kmiku7/sarama