Some more documentation for pickneglogsoftmax etc.
Some more documentation for pickneglogsoftmax etc.


Former-commit-id: d219cdd1d37fc83b10fdacad2ba3e5aa885e6439
shuheik/dynet,clab/dynet,chunyang-wen/dynet,clab/dynet,shuheik/dynet,xunzhang/dynet,clab/dynet,danielhers/dynet,clab/dynet,danielhers/dynet,clab/dynet,xunzhang/dynet,danielhers/dynet,danielhers/dynet,xunzhang/dynet,clab/cnn,chunyang-wen/dynet,clab/dynet,shuheik/dynet,clab/cnn,shuheik/dynet,chunyang-wen/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,chunyang-wen/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,clab/cnn,clab/dynet,xunzhang/dynet