Update language reference link

This PR is not intended to be merged, but rather to discuss the situation with the language specification. The currently linked spec is pretty outdated (2.8). Are there any plans to update the specification to the latest language state (2.10), or at least link to the latest available spec (2.9)?

Related work:
* https://github.com/scala/scala-dist/pull/20
* http://iainmcgin.github.io/scala-ref-markdown/
* https://github.com/iainmcgin/scala-ref-markdown/tree/2.10
* https://github.com/iainmcgin/scala-ref-markdown/tree/2.11

*P.S.* Congratulations, the site looks gorgeous :+1: 
/cc @soc @adriaanm @Blaisorblade @odersky