Begin to support CTC models (#119)

Please see https://k2-fsa.github.io/sherpa/onnx/pretrained_models/offline-ctc/nemo/index.html for a list of pre-trained CTC models from NeMo.

sherpa-onnx/python/csrc/offline-nemo-enc-dec-ctc-model-config.cc

@@ -0,0 +1,22 @@
+// sherpa-onnx/python/csrc/offline-nemo-enc-dec-ctc-model-config.cc
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#include "sherpa-onnx/python/csrc/offline-nemo-enc-dec-ctc-model-config.h"
+
+#include <string>
+#include <vector>
+
+#include "sherpa-onnx/csrc/offline-nemo-enc-dec-ctc-model-config.h"
+
+namespace sherpa_onnx {
+
+void PybindOfflineNemoEncDecCtcModelConfig(py::module *m) {
+  using PyClass = OfflineNemoEncDecCtcModelConfig;
+  py::class_<PyClass>(*m, "OfflineNemoEncDecCtcModelConfig")
+      .def(py::init<const std::string &>(), py::arg("model"))
+      .def_readwrite("model", &PyClass::model)
+      .def("__str__", &PyClass::ToString);
+}
+
+}  // namespace sherpa_onnx