* Optimize softmax. When the input tensor is 2-D and axis is 1, there is no need to resize.

* Optimize the gru, avoid calling Tensor::Slice.
test=develop

* Remove a std::vector in softmax.
test=develop

* Define CalculateSeqWidth to get the width of a sequence.
test=develop

-fix fluid-lite-subgraph x86 compile error
    - Replace FLAGS with environment variables

* add x86 gru&&relu&&sequence_expand_as op test=develop