ais.h assigned_mode is type int for messages 9 & 19, boolean for type 21

[kiwibrew]

My reading of ITU-R M.1371-5 assigned_mode is that it's a boolean variable. This (fantastic and much appreciated) decoder treats assigned_mode as type int for messages 9 & 19, and type boolean for message 21. It'd be super awesome if it could be either boolean or int for all three message types. Is it just a matter of changing ais.h, or are there other parts of the application that would need updating?

[kiwibrew]

Hi, just asking for advice here so I know where to start.