[Feature Request] An API to directly enter bopomofo into ChewingContext

[school510587]

I am developing an input method called 點字酷音 (Braille Chewing) based on PIME with @PCMan and other participants. 點字酷音 detects braille input from the user, which may not be represented as a single keyboard layout. After recording the braille input, 點字酷音 converts it into bopomofo sequences. I think that it is intuitive to send bopomofo symbols directly to libchewing. However, libchewing currently does not support any API to achieve this. It always requires character codes defined by some specific keyboard layout. Thus, I think libchewing needs an API to append bopomofo symbols into the bopomofo buffer.