Document features

### Mdict

- [spec](https://mdict4j.readthedocs.io/zh-cn/latest/reference/fileformat.html)
- [mdict-utils](https://github.com/liuyug/mdict-utils)
- [goldendict parser](https://github.com/xiaoyifang/goldendict-ng/blob/staged/src/dict/mdictparser.cc)


### Stardict

- Doesn't compress the dict file

### Yomitan

- [repo](https://github.com/yomidevs/yomitan)
- [schemas](https://github.com/yomidevs/yomitan/tree/master/ext/data/schemas)
- [fixtures](https://github.com/yomidevs/yomitan/tree/master/test/data/dictionaries/valid-dictionary1)
- [ts schemas](https://github.com/MarvNC/yomichan-dict-builder/tree/master/src/types/yomitan)
  - [term bank](https://github.com/MarvNC/yomichan-dict-builder/blob/master/src/types/yomitan/termbank.ts#L35)
