At least in the caller perspective.
Also break down some functionalities into separate funcs,
interally calling them on cert.c to avoid too many checks.
And tried to avoid too much repeated code.
Except for cia building or loading cia just yet.
Added more checks on ticket content index, mainly due to having effects
in the ticket format itself, and are unknown still.
Ability to determine ticket size.
Verify signature with ticket's proper size.
Changes to use the new Ticket struct with the flexible array member.
