add juju-ha link and rename "High Availability" to "Charm High Availability"

remove info about Juju HA from Charm HA page and make a new page for Juju HA.
URL tweaking to reference exact relation hooks. Dropped some notes regarding bugs that have been resolved for some time. Note in authors-charm-hooks was broken, syntax changed to reflect Juju markdown syntax. Changed authors-charm-hooks references to hooks, such as -joined, to make it more obvious / stand out more against the paragraphs and walls of text. Dropped hook-kinds since it was just an outdated version of charm-hooks.
Merge pull request #176 from JoshStrobl/master

URL tweaking to reference exact relation hooks. Dropped some notes regarding bugs that have been resolved for some time.
Fixes incorrect use of angle brackets that get interpreted as HTML
Merge pull request #177 from chuckbutler/fix_html_rendering

Fixes incorrect use of angle brackets that get interpreted as HTML
Fixed links to references of exact hooks.
Merge pull request #178 from JoshStrobl/master

Fixed links to references of exact hooks.
Merge pull request #174 from natefinch/master

Move juju HA into it's own topic
Incorporating review suggestions.
Merge branch 'master' of https://github.com/juju/docs into unmaintained-charms