PROTON-538: fixed install to not use irregular paths, marked a lot of noisy variables as advanced, removed extra level of caching from cmake variables that had confusing effects, updated the readme to match what the build actually does

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1582416 13f79535-47bb-0310-9956-ffa450edef68