LGTM -- thanks@prantlf ! I'll look forward to the docs merged next. :)

Let's see. I'm going to have a look at the cpp-netlib documentation structure, but before "going wild" with the programmer's guide I wanted to try the two possibilities how to design the API - separate function templates or one class template. I tried to continue with the separate functions in thebase64_util_function_templates branch and not being able to typedef the specialization is annoying me:

std::string result = base64::encode<base64::normal, char>("...");std::back_insert_iterator<std::string> result_encoder(result);base64::encode<base64::mime>("...", std::back_inserter(encoder), rest);...base64::encode_rest<base64::mime>(encoder, rest);std::stringstream output;output << base64::io::encode<base64::normal>("abc") <<      base64::io::encode_rest<base64::normal, char>;

I'd like to try the static class approach and see what will annoy me there :-)