> I think RUBY_API_VERSION should be 2.0.0 for Ruby2.0.0.
> In other hand, some people might think it should stay 1.9.1 becouse Ruby2.0.0 will have backward compatibility with 1.9.

Please just bump it up now. I can imagine people want to install both
1.9.3 and 2.0.0 a while.