Node 0.10.x compatibility

Hello,
this pull request tries to address node 0.10 compatibility.

There are still few warnings though, I'm unsure how to proceed.

```
../src/taglib.h:22:22: warning: unused function 'createFile' [-Wunused-function]
static TagLib::File *createFile(TagLib::IOStream *stream, TagLib::String format);

../src/tag.cc:17:20: warning: unused function 'now' [-Wunused-function]
static suseconds_t now()

../src/taglib.cc:296:1: warning: control reaches end of non-void function [-Wreturn-type]
}
```