Fix and clarify RDoc for Dataset#group_and_count
Fix and clarify RDoc for Dataset#group_and_count

bigfix/sequel,pfarrell/sequel,t-morgan/sequel,seeARMS/sequel,freshpay/sequel,freshpay/sequel,nicohvi/sequel,yazshel/sequel,offshore-safety/sequel,nju520/sequel,reubano/sequel,t-morgan/sequel,davidbegin/sequel,gferguson-gd/sequel,knut2/sequel,dennis-d/custom_sequel,mpalmer/sequel,beni55/sequel,yazshel/sequel,gferguson-gd/sequel,Marketcircle/sequel,pfarrell/sequel,offshore-safety/sequel,beni55/sequel,nicohvi/sequel,mpalmer/sequel,knut2/sequel,offshore-safety/sequel,chef/sequel,reubano/sequel,uhoh-itsmaciek/sequel,uhoh-itsmaciek/sequel,tmm1/sequel,nju520/sequel,seeARMS/sequel,dennis-d/custom_sequel,davidbegin/sequel