Fixed conversion from empty String to ByteVector
Remove a superfluos 'x'
Merge pull request #340 from mineo/patch-1

Remove a superfluos 'x'
Use std::string::c_str() rather than &s[0] where a const pointer is required.
Avoid using &d->data[0] when d->data is empty.
Merge pull request #330 from TsudaKageyu/fix-emptystring

Fixed a bug reported at #328
Changed XM::File::save() to use seek() properly.
Merge pull request #347 from TsudaKageyu/xm-seek

Changed XM::File::save() to use seek() properly.
Enable read-only file support