- add yycc_char8_t and yycc_u8string in code to indicate explicit utf8 char type and string. it also has a polyfill if compiler and library do not support utf8 char type.
- refactor the whole encoding helper. allow converting string with embedded NUL. but not tested.
- use configuration-arch-based path in MSVC to make sure generated package can be used by native MSVC project.
- add github action and corresponding build script. but not tested.
- fix some testbench code.
