Japanese: create a branch to test out the feasibility of certainty detection

[makorin0315]

This issue came out of a conversation with @Rei-hub and Dr. Torikai from Gunma University Hospital on February 9th, 2022 JST.

Certainty detection sounds like a very promising feature, but it is not clear yet how it would look in Japanese due to the nature of the language.

If we are to take the same steps we took to implement Certainty detection in English, it would require:

1. additional expansion capabilities, i.e., more PathRelevant entity identification
2. Identification of common Certain vs. Uncertain words/expressions
3. User Dictionary - which currently is not supported in Japanese
4. Implementation of relevant rules

However, to determine if this would be a useful feature in Japanese or not, we would like to do a experiment with a small set of changes in the language model. For this, we would implement a subset of steps 1, 2 and 4 above in a branch, and test against some radiology report text.