pick and pickrange as indexing.
pick and pickrange as indexing.


Former-commit-id: 5dd7f86dd507300d86d82215cb1c0afe18536787
clab/dynet,chunyang-wen/dynet,chunyang-wen/dynet,clab/cnn,clab/dynet,chunyang-wen/dynet,danielhers/dynet,shuheik/dynet,danielhers/dynet,shuheik/dynet,xunzhang/dynet,clab/dynet,clab/dynet,danielhers/dynet,clab/dynet,danielhers/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,xunzhang/dynet,shuheik/dynet,xunzhang/dynet,danielhers/dynet,chunyang-wen/dynet,clab/cnn,danielhers/dynet,xunzhang/dynet,shuheik/dynet,clab/dynet,clab/cnn,shuheik/dynet,clab/dynet