Load a language model and decode with it during evaluation

Based on !346 (merged)

Closes #252 (closed)

docs/usage/train/config.md

@@ -66,7 +66,7 @@ You should get the following tree structure:
 
 ```
 folder/
-├── `model.lm.path` # Path to the language model
+├── <model.lm.path> # Path to the language model
 ├── lexicon.txt
 └── tokens.txt
 ```