Search Chinese by the first letter of Chinese pinyin.
使用拼音首字母搜索中文。
e.g. use `zw` to search `中文` (*Z*hong *W*en).

Usage:

- `isearch-forward-pinyin'
- `isearch-backward-pinyin'

or run `isearch-toggle-pinyin' (`M-s p') after invoking any normal
`isearch' commands like `C-s` (`isearch-forward`).

Known Bugs and Limitations:
- [anzu.el](https://github.com/syohex/emacs-anzu) compatibility