Add link formatting to Velocity comments

For example the rule

  [rule "formatLinkSampleRule"]
          event-type = comment-added
          action = add-velocity-comment inline Comment for change $change-number added. See ${its.formatLink($change-url)}

would format a link to the event's change-url in the its' syntax.

Change-Id: Ic3b4a13913309719c34ed1e66a9acdf246096522