Cross build scalahost-runtime with 2.8 to 2.11

Cross build scalahost-runtime with Scala 2.8.2, 2.9.2, 2.9.3, 2.10.4
and 2.11.0 (the versions against which SBT is compiled).

I've not been able to automate the "cross publishing", and I have found no example of it done anywhere. To cross publish [locally] :

```
sbt "project scalahost-runtime" "+ publish[Local]"
```