* pass const `char32_t` array and `QETermStyle` array to `ColorizeFunc`
* add `cp_colorize_line()` wrapper to call colorizer function on null
terminated buffer.
* remove unused `EditBuffer` colorize fields
* remove `EditState` field `colorize_func`: rely on `colorize_mode` only
* no longer combine style into codepoint buffer.
* remove `STYLE_BITS`, `STYLE_SHIFT`, `CHAR_MASK`
* rename `set_colorize_func` as `set_colorize_mode`
* rename `SET_COLOR` and `SET_COLOR1` as `SET_STYLE` and `SET_STYLE1`
* add documentation for buffer API functions
