[BUGFIX] branchToRelease accessing wrong array
[FEATURE] Only add valid release to the list of 'planned'
[FEATURE] Added perReleaseOutput option

This will create pages like "core-6.2.html" which list only the
unique new features on each release. So this list won't include
any issue which was also backported to some older version.

The list helps the release manager to know what's *relly* new in
a particular release. :)