feat: exists to return the type of a path

[wassup05]

User facing stuff added are

• integer function exists (path [, err]) to check if a file exists and return it's type.
• integer parameters, type_unknown, type_regular_file, type_directory, type_symlink which are the return values of the exists function.

To accomplish this, on unix lstat is used and on windows GetFileAttributesA is used.

1. If any errors, type_unknown is returned
2. the code and the string describing the code are provided through FS_ERROR_CODE (using strerror on unix and FormatMessageA on windows).
3. and to accomplish this platform based error handling c_getstrerr now takes a logical winapi argument to switch between these two functions (strerror and FormatMessageA).