Hash expression

Add md5 hash expression operator as requested by @billhowe. If needed, we can easily add consistent hashing. This pr also updates janino. 

Needs implementation in raco as well. @7andrew7. 
interesting. Does this somehow add sandboxing, or does this just let you skip the full classpath? Note that we [used the full classpath elsewhere](https://github.com/uwescience/myria/blob/master/src/edu/washington/escience/myria/expression/PlusExpression.java#L39):

```java
  @Override
  public String getJavaString(final ExpressionOperatorParameter parameters) {
    Type t = getOutputType(parameters);
    if (t == Type.INT_TYPE) {
      return getFunctionCallBinaryString("com.google.common.math.IntMath.checkedAdd", parameters);
    } else if (t == Type.LONG_TYPE) {
      return getFunctionCallBinaryString("com.google.common.math.LongMath.checkedAdd", parameters);
    }
    return getInfixBinaryString("+", parameters);
  }
```