I've added some functionality to wolfSSL that allows the developer
to hook in their own log interceptor function.

To facilitate this I moved some code from cyassl_int.h & cyassl_int.c
into the new files logging.h & logging.c
I'm not sure whether these are the most suitable names for the new files ?

By default the behaviour will remain as before, however if an interceptor
is registered, log messages will  instead be routed there.

The other change was the addition of an enum[CYA_Log_Levels]
to map log levels. This is useful for filtering out uninteresting messages;
the case where a developer only cares about errors for example.

Eoin ó Fearghail, Agora Games.