#181 Use ID3_Writer for Unicode filenames

[Spitfed]

The first responder should have mentioned that you'd also need to derive a class from ID3_Writer if you'd like to write a file using a Unicode filename.

Unicode support in Id3lib is very shakey. ID3TE_UTF16BE doesn't function, forcing the use of ID3TE_UTF16 which, on Windows platforms, is a nuisance (reversed bytes). Non-Unicode filenames on top of this, is a right ball-ache.

Thanks for the library anyway - the rest of functionality is much appreciated.