add docs

doc for inverted topN metric spec
a few more cleanups to docs
Merge pull request #646 from metamx/inverted-topn-metric-spec-docs

add docs
fix config with broker select and add docs
Merge branch 'master' of github.com:metamx/druid
a few slight tweaks and bumping up curator version
add query priorities to metric emission
completely async request proxying + jetty update