libconfig: Allow user to select output format types

According to BNF grammar trailing each line with ; is optional,
so user should be allowed to select if ; should be placed
in output of library or not.

Similar situation is with : and =. In grammar they are
considered to be equivalent but when using library to export
the config there is some policy which determines which one
should be used. In this situation user should be able to
enforce than one of them should be used in all cases.

Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>

Changes:
I have edited this message and commit message to fix all spelling mistakes. Sorry for them.
 Do you suggest that formatting options should be global not per setting node or I'm missing something? Why not use the same model as here in hex/decimal? Allow to set it globally but also allow  setting nodes to override formatting options individually? To be honest, I don't urge that such model should be used because the one you suggested (with only global formatting flags) fulfils my use case;) I would like only to know your argumentation.