Use UTF-8 string directly instead of hex string

[czchen]

Hex string is used for UTF-8 string due to Visual Studio. However, according to this, we can use #pragma execution_character_set("utf-8") to let Visual Studio uses UTF-8 encoding. In this way, we might be able to avoid ugly hex string.

[czchen]

Need to test in Windows.

[czchen]

See #37. Currently we cannot build chewing-editor in Windows due to C++11 features.

[Chocobo1]

I've encountered this bug before (in qBittorrent).
The solution ended up moving all UTF8 strings to a file and encode the file with UTF-8 (with BOM) and also adding the #pragma.
See: https://github.com/qbittorrent/qBittorrent/blob/master/src/base/unicodestrings.h

If you find this solution acceptable, I can help implement this.