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 doc/release-notes/1.6

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Update doc/user-guide/1.6

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

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