Support various Chinese input methods

[diskdance]

Support Chinese IMEs like Pinyin, Wubi and Bopomofo (Zhuyin), Cangjie.

Chinese IMEs are very complex. They usually include candidate lists, and the logic is too complicated to describe with existing methods in this repo.

Google's input tool has Chinese support, but candidate lists are generated on the server side, which is not appropriate I believe due to privacy concerns.

The most feasible solution I can come up with is to use and compile librime, a popular Chinese IME engine, to WebAssembly. (there's already an implementation here)