Update doc/release-notes/1.4

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Update doc/release-notes/1.5

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
update-site: Add 1.6 doc
Update doc/release-notes/1.6

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Set doc/release-notes/1.6 as current

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>