Made max pooling 2d be able to take in 2d tensors (#1065)
Made max pooling 2d be able to take in 2d tensors (#1065)

* Made max pooling 2d be able to take in 2d tensors

* Fixed copying of dimension

clab/dynet,clab/dynet,danielhers/dynet,clab/cnn,clab/dynet,clab/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,shuheik/dynet,xunzhang/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,clab/cnn,chunyang-wen/dynet,shuheik/dynet,danielhers/dynet,xunzhang/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet,chunyang-wen/dynet,danielhers/dynet,chunyang-wen/dynet,xunzhang/dynet,xunzhang/dynet,clab/cnn