Add Cangjie 3 code "raiu" for character "嘅"

The character "嘅" has a different glyph in different Chinese
standard. The mapping to `口日戈山` ("raiu") makes better sense
for the Hong Kong glyph standard.

The mapping exists in Cangjie 5 already. It is now added to Cangjie
3 also.

Fixes #93.