Stack and streaming conformer support (#141)

* added csrc/stack.cc

* stack: added checks

* added copyright info

* passed cpp style checks

* formatted code

* added some support for streaming conformer model support (not verified)

* code lint

* made more progress with streaming conformer support (not working yet)

* passed style check

* changes as suggested by @csukuangfj

* added some debug info

* fixed style check

* Use Cat to replace Stack

* remove debug statements

---------

Co-authored-by: Jingzhao Ou (jou2019) <jou2019@cisco.com>
Co-authored-by: Fangjun Kuang <csukuangfj@gmail.com>

sherpa-onnx/csrc/CMakeLists.txt

@@ -34,6 +34,7 @@ set(sources
   offline-transducer-model-config.cc
   offline-transducer-model.cc
   offline-transducer-modified-beam-search-decoder.cc
+  online-conformer-transducer-model.cc
   online-lm.cc
   online-lm-config.cc
   online-lstm-transducer-model.cc
@@ -52,6 +53,7 @@ set(sources
   parse-options.cc
   resample.cc
   slice.cc
+  stack.cc
   symbol-table.cc
   text-utils.cc
   transpose.cc
@@ -241,6 +243,7 @@ if(SHERPA_ONNX_ENABLE_TESTS)
     packed-sequence-test.cc
     pad-sequence-test.cc
     slice-test.cc
+    stack-test.cc
     transpose-test.cc
     unbind-test.cc
   )