Updated backup-restore howto

Updated backup-restore howto to reflect current state of
the process for HA
Merge branch 'master' of https://github.com/juju/docs
Added high availability docs

Added the ensure-availability command to the commands list
Added a brief howto on how to use ensure-availability
Add Charm Helpers page with link to docs
Merge pull request #125 from tvansteenburgh/charm-helpers

Add Charm Helpers page with link to docs
Update 'charm create' docs with new template stuff
Add section for create options
Merge pull request #126 from tvansteenburgh/charm-create-templates

Update 'charm create' docs with new template stuff
Merge pull request #112 from perrito666/add_HA_howto

Added high availability docs
Merge pull request #107 from perrito666/master

Updated backup-restore howto
/Using charms/Using Juju
Added debug-log documentation.
Switch contraints reference to list format because the conversion of definition list to markdown created bogus code examples.
Add High Availability page.
Add actual HA docs.
Fix note and wrap long lines in reference-constaints.
Update constraints reference to 1.20.0

- Move instanct-type back to current constraints.
- Add the network constrain
- Add an explanation of constraints based on the help.
Fixed punctuation.
Merge pull request #129 from abentley/add-ha

Add ha
Merge pull request #128 from sinzui/constraint-cleanup

Switch contraints reference to list format