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

.github/workflows/run-python-test.yaml

@@ -54,7 +54,7 @@ jobs:
       - name: Install Python dependencies
         shell: bash
         run: |
-          python3 -m pip install --upgrade pip numpy
+          python3 -m pip install --upgrade pip numpy sentencepiece==0.1.96
 
       - name: Install sherpa-onnx
         shell: bash