follow up librime#806, avoid path-string conversion

[lotem]

Avoid using RimeGet*Dir() from rime_api. They return native path on Windows and coding conversion is incurred.

When passing path from lua to librime class, use either rime::path object or UTF-8 encoded string.

[lotem]

還有一小部份 ，可否一起

These changes are in my commit. Anything else?

[lotem]

Changed file_name(db) to return ANSI string. PTAL

[hchunhui]

LGTM. Added some code to ensure it can build with librime <= 1.9.0