[feature request] 更多 anthy 功能

Reference: http://www.h4.dion.ne.jp/~apricots/scim-anthy/howto.html

1. gcin 尚未實作的 hotkeys:

隱F8 = 把 buffer 內容轉成 half-width characters (half-width Katakana or regular Latin alphabets depending on the previous state)

隱Shift+F8 = 把 buffer 內容轉成 half-width Katakana

隱F9 = 把 buffer 內容轉成 wide-width Latin alphabets

隱F10 = 把 buffer 內容轉成 regular Latin alphabets

隱F6 = 把 buffer 內容轉成 Hiragana

隱連續按下 F9 或 F10 = buffer 內容轉換大小寫，例如 home > HOME > Home.

2. 片假名模式 (直接輸入全形或半形片假名，不用按 space)

隱Ctrl+period = cycles through three Japanese input modes i.e. Hiragana, Katakana and Half-width Katakana

隱Ctrl+comma = cycles through all including Latin and Wide Latin.