Implement context biasing with a Aho Corasick automata (#145)

* Implement context graph

* Modify the interface to support context biasing

* Support context biasing in modified beam search; add python wrapper

* Support context biasing in python api example

* Minor fixes

* Fix context graph

* Minor fixes

* Fix tests

* Fix style

* Fix style

* Fix comments

* Minor fixes

* Add missing header

* Replace std::shared_ptr with std::unique_ptr for effciency

* Build graph in constructor

* Fix comments

* Minor fixes

* Fix docs

sherpa-onnx/csrc/offline-recognizer-transducer-impl.h

@@ -10,6 +10,7 @@
 #include <utility>
 #include <vector>
 
+#include "sherpa-onnx/csrc/context-graph.h"
 #include "sherpa-onnx/csrc/macros.h"
 #include "sherpa-onnx/csrc/offline-recognizer-impl.h"
 #include "sherpa-onnx/csrc/offline-recognizer.h"
@@ -72,6 +73,16 @@ class OfflineRecognizerTransducerImpl : public OfflineRecognizerImpl {
     }
   }
 
+  std::unique_ptr<OfflineStream> CreateStream(
+      const std::vector<std::vector<int32_t>> &context_list) const override {
+    // We create context_graph at this level, because we might have default
+    // context_graph(will be added later if needed) that belongs to the whole
+    // model rather than each stream.
+    auto context_graph =
+        std::make_shared<ContextGraph>(context_list, config_.context_score);
+    return std::make_unique<OfflineStream>(config_.feat_config, context_graph);
+  }
+
   std::unique_ptr<OfflineStream> CreateStream() const override {
     return std::make_unique<OfflineStream>(config_.feat_config);
   }
@@ -117,7 +128,8 @@ class OfflineRecognizerTransducerImpl : public OfflineRecognizerImpl {
                                -23.025850929940457f);
 
     auto t = model_->RunEncoder(std::move(x), std::move(x_length));
-    auto results = decoder_->Decode(std::move(t.first), std::move(t.second));
+    auto results =
+        decoder_->Decode(std::move(t.first), std::move(t.second), ss, n);
 
     int32_t frame_shift_ms = 10;
     for (int32_t i = 0; i != n; ++i) {