Unidecode for `std::string`

[marekru]

Create version of the Unidecode function which takes std::string as an argument.

Usage:

std::string decoded = Unidecode( u8"mačka" )

Example implementation:

auto Unidecode(... utf8_string)
{
    std::string result;
    unidecode::Utf8StringIterator begin{utf8_string.c_str()};
    unidecode::Utf8StringIterator end{utf8_string.c_str() + utf8_string.length()};
    unidecode::Unidecode(begin, end, std::back_inserter(result));
    return result;        
}