Suggestion: some changes in String API

I suggest to make some small changes in ```String``` API.
Currently, ```String``` class has some methods which convert itself into a standard C/C++ string, but they are somwhat confusing and inconsistent. So I'd like to change these methods:
```
// Current
std::string to8Bit(bool unicode = false) const;
const std::wstring &toWString() const;
const char *toCString(bool unicode = false) const;
```
like this:
```
// New
std::string toStdString(Type t = Latin1) const;
const std::wstring &toStdWString() const;
const char *toCString(String::Type t = Latin1) const;
```
I think that toCString() is no longer needed and can be substituted by toStdString() so we can remove it.