Document the policy-based versions of for_each & for_each_n.
Document the policy-based versions of for_each & for_each_n.

marksantos/thrust,jaredhoberock/thrust,thrust/thrust,Ricardo666666/thrust,dachziegel/thrust,dachziegel/thrust,thvasilo/thrust,thrust/thrust,zeryx/thrust,zhenglaizhang/thrust,raygit/thrust,Ricardo666666/thrust,jaredhoberock/thrust,andrewcorrigan/thrust-multi-permutation-iterator,thrust/thrust,raygit/thrust,thrust/thrust,sdalton1/thrust,sarvex/thrust,sdalton1/thrust,Ricardo666666/thrust,sdalton1/thrust,egaburov/thrust,arnabgho/thrust,sarvex/thrust,dachziegel/thrust,xiongzhanblake/thrust,thvasilo/thrust,thvasilo/thrust,GrimDerp/thrust,raygit/thrust,zhenglaizhang/thrust,thrust/thrust,xiongzhanblake/thrust_src,xiongzhanblake/thrust_src,arnabgho/thrust,xiongzhanblake/thrust_src,mohamed-ali/thrust,sarvex/thrust,zeryx/thrust,zhenglaizhang/thrust,GrimDerp/thrust,jaredhoberock/thrust,xiongzhanblake/thrust,jaredhoberock/thrust,arnabgho/thrust,zeryx/thrust,andrewcorrigan/thrust-multi-permutation-iterator,jaredhoberock/thrust,egaburov/thrust,mohamed-ali/thrust,mohamed-ali/thrust,marksantos/thrust,egaburov/thrust,marksantos/thrust,xiongzhanblake/thrust,GrimDerp/thrust,andrewcorrigan/thrust-multi-permutation-iterator