Allowed transitions (#5706)

* Add allowed_transitions in __init__.py of crf mod.

Fix ImportError:
from allennlp.modules.conditional_random_field import allowed_transitions
ImportError: cannot import name 'allowed_transitions' from 'allennlp.modules.conditional_random_field'

* Fix doc build

Co-authored-by: Chengjiang Li <iamlockelightning@gmail.com>

.github/workflows/ci.yml

@@ -515,7 +515,7 @@ jobs:
     - name: Build docs
       run: |
         source .venv/bin/activate
-        ./scripts/build_docs.sh
+        env PYTHONPATH=. ./scripts/build_docs.sh
 
     - name: Print the ref
       run: |

allennlp/modules/conditional_random_field/__init__.py

@@ -1,5 +1,6 @@
 from allennlp.modules.conditional_random_field.conditional_random_field import (
     ConditionalRandomField,
+    allowed_transitions,
 )
 from allennlp.modules.conditional_random_field.conditional_random_field_wemission import (
     ConditionalRandomFieldWeightEmission,