Impala docs now included in CDH 5 library

With the release of CDH 5.0.0 and Impala 1.3.0, now for the first time the Impala docs are embedded alongside the CDH Installation Guide, Security Guide, and other CDH docs. This integration makes it easier to link back and forth both ways, and also will help readers find Impala-related content when they search within the CDH 5 library. Here's the full layout of the CDH 5.0.0 library. Notice