Added basic doc for HA
Added singleton and voting sections and corrected

I addressed several redaction issues and added sections for
voting and singleton workers as commented by @rogpeppe
Made gramatical corrections suggested by @mjs
Added note on singleton vs concurrent

After talking with @fwereade I added a note explaining that
singletons, as they are documented righ now, are only a reflection
of current status but should be considered as wrong and will be
re-implemented properly, as concurrent workers, in the future.
Corrected two gramatical errors
wip, state objects now return a Tag not a string.
Ensure availability command output.
Report result type error.
Json encoding specifiers for api structs.
Rename EnsureAvailabilityParams to StateServersSpec.
Rename EnsureAvailabilityResult to StateServersChange.
State EnsureAvailability call returns changes structure.
Added promotion and demotion information to ensure-availability output.
Tag-Id separation in ensure-availability.
Tags instead of ids.
Minor cleanup.
Do not quote machine names.
Updates w.r.t new names package api.
Merge pull request #39 from tasdomas/ensure-availability-output

Ensure availability command output.

Add output for ensure-availability command.

The ensure-availability command will notify the user, how many state servers
were added to the environment.

$ juju ensure-availability -n 7
maintaining machines: "0"
adding machines: "1", "2", "3", "4", "5", "6"

This is a move to github of the MP started in https://codereview.appspot.com/99670044/
Merge pull request #30 from perrito666/update_HA_doc

Added basic doc for HA

I created a doc for High Availability based on code analysis and interviewing people from the team that where involved in the design and development of this.
Update to latest juju/names