Refactor tokenization

So that we can instantiate tokenization before we know what dataset we want to use it on. Previously it was tidly copuled.

README.md

@@ -12,3 +12,9 @@ You can evaulate any model with the following command:
 ```bash
 python -m ulmfit load data/mldoc/de-1/models/fsp15k/multfit_fp16 classifier validate data/mldoc/de-1
 ```
+
+
+```bash
+python -m ulmfit new multifit_fp16_nl3 pretrain-lm train- data/wiki/wikitext-103
+
+```