title: C++ convert ASII escaped unicode string into utf8 string
body: <p>I need to read in a standard ascii style string with unicode escaping and convert it into a std::string containing the utf8 encoded equivalent. So for example "\u03a0" (a std::string with 6 characters) should be converted into the std::string with two characters, 0xce, 0xa0 respectively, in raw binary.</p>
  
  <p>Would be most happy if there's a simple answer using icu or boost but I haven't been able to find one.</p>
  
  <p>(This is similar to <a href="https://stackoverflow.com/questions/1615559/converting-unicode-strings-to-escaped-ascii-string">Convert a Unicode string to an escaped ASCII string</a>, but NB that I ultimately need to arrive at the UTF8 encoding. If we can use the Unicode as an intermediate step that's fine.)</p>