2. Add crop layer unitest
3. Fix bugs

* We should not EXPECT_EQ between a float value and a int value.
  Use ASSERT_NEAR instead.

1. change configure content to 'axis, offset, shape'
2. add an optional input to crop layer as cropping reference

1. change configure content to 'axis, offset, shape'
2. add an optional input to crop layer as cropping reference

Add the use_nnpack parameter in ExpandConvLayer, so that the convolution calculation can be switched to the NNPACK function.

Fix #2567

Change the CpuMatrix::copyFrom and CpuVector::copyFrom with the stream parameter to the synchronous interface.

Please use `override` not `virtual` in sub-classes.
`override` can check if there is a method in `parent` while compiling.

Make the evaluators inside a recurrent goup true evaluator, meaning that their evaluation results are incorporated into the whole evaluator result.

1. v2.layer.parse_network does not correctly handle the generation output.
2. GatherAgentLayer does not correctly handle generation output when batch_size > 1
3. Fix CustomStackTrace for rnn group

For example:
layer.printer(input=[x, y], format="x=%s y=%s")

No longer need to specify target_inlinks or is_seq.