Rebuild

This is a pretty major rewrite of our code. 

I have taken several steps:

1. I have removed the concept of "rule reversal" for now. This turned out to involve a lot of annoying filename manipulation, and also raised hairy questions of how to validate whether a particular ruleset really was "reversible". Rather, the "contributed" form of *each* transliteration scheme should now begin life as a `.txt` file in the "textual" format. 
2. I have unified the `.py` files which were in the `rules/` directory into a top-level `rebuild_data.py` file in the top level. This still needs to be documented. 
3. The `rules/test/` directory has been moved to the top level. We should think about how to implement proper tests in the future, but it seems simpler to keep only language transliteration rules under `rules/`.
4. I merged the subdirectores `rules/japanese/hiragana/` and `rules/japanese/katakana`. This simplified the directory traversal logic in `rebuild_data.py`.  

If you would like to just take a look at this rewrite, make sure everything is committed in your working directory, and then do:

    git pull origin rebuild

And then:

    git checkout rebuild

When you are done looking around at my proposed changes, you can run:

    git checkout master

And you will be back in your own working directory. If we all agree to the proposed changes here, we can can `merge`  the `rebuild` branch into the `master` branch, and then we will all be on the same page again.