Running `highlight -O truecolor test.cpp` throws
> cannot open filetypes.conf: No such file or directory
> highlight: cannot open themes\edit-vim-dark.theme: No such file or directory
since highlight.exe expects `themes/`, `langsDefs/` and `plugins/`
directories to be under the same directory as `highlight.exe` on
Windows.
* Add `HL_DATA_DIR` and `HL_CONFIG_DIR` to possible search directories
even if `_WIN32` is defined.
* Workaround [MinGW bug #810][1] where `stat()` reports directory as
missing when there’s a trailing slash in path
- This is needed for `--list-scripts` option to work
* Remove binary path from possible search directories since in MSYS2
systems the `/bin` directories never have assets.
[1]: https://sourceforge.net/p/mingw-w64/bugs/810/
