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.
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