[Backport] some docs PRs#2732

Merged

fjy merged 3 commits intoapache:0.9.0from

gianm:backport-docs

Mar 28, 2016

Commits on Mar 25, 2016

Improved docs for multi-value dimensions.
gianm
committed

Commits on Mar 28, 2016

refactor extensions into their own docs

fjy
authored and
gianm
committed
Fix a bunch of broken links in the docs.
gianm
committed