links&formatting in the Configuring The Cache Docs

* in particular, we also document the change brought by TS-1994, that the
RAM Cache Size now is 10x bigger than before.
* Along with the changes to this document, we fix up volume.config and
storage.config, which are strongly linked: We take care to consistently
use the group Unix `tserver` instead of mixing random groups.

unrelated to this, we fix-up the syntax of .. note:: and .. important::

TODO: The getting started documentation should strongly recommend users
to create a dedicated Unix user for Apache Traffic Server rather than
`nobody:nogroup`. We should recommend `tserver` and consistently in the
documentation use `tserver:tserver`.
fix links&formatting in monitoring traffic docs

notes: *someone* seems to have deleted the traffic_shell docs, I'm
suspecting @igalic

:program:`traffic_line` has loads of performance variables that need
to be documented.. Volunteers?

We're missing docs on how to use tstop.  @dcarlin volunteered for this