symbol parsing bug has been fixed

In my opinion, maybe rbyaml is ported from pyyaml. And in Python, there is no symbol class. So rbyaml doesn't support symbol parsing at first.

This week, I worked on symbol parsing bug. I spent lots of time on tracking the stream parsing flow with ruby-debug. During the tracking process, I added some spec tests to cover the method call stack.
After I find out the fixing solution. Then I found that bug had been fixed already in rubinius. It really helped me a lot.
Now, RbYAML can parse stream which inlcude symbol smoothly.
You can try it by following code.

RbYAML.load("---\n :firstname: Long\n lastname: Sun")
=> {:firstname=>"Long", "lastname"=>"Sun"}