lib/dstat: Include page stats

Add -g option for dstat.

From the man page:

       -g, --page
              enable page stats (page in, page out)

Change-Id: I865304483af0a529ea8722ed0a9f35ab350670d2
add LIBS_FROM_GIT to docs

Also reformat common configuration variables to have an additional
header level which makes it easy to direct link to specific
configuration vars when directing someone.

Reformat header markup to us a more standard == = - for h1, h2, h3

Change-Id: I10bac5a93529cdfbcde0a05f9ebdbc1799d403cd
Merge "add LIBS_FROM_GIT to docs"
Merge "lib/dstat: Include page stats"
Merge branch 'master' of https://github.com/openstack-dev/devstack