Add exception handling information
code - exception code
name - exception name
desc - exception description
flags - exception flags (combination of EXC_...)
returns: failure description or ""
string define_exception(long code, string name, string desc, long flags);
#define EXC_BREAK 0x0001 // break on the exception
#define EXC_HANDLE 0x0002 // should be handled by the debugger?
#define EXC_MSG 0x0004 // instead of warn, log the exception to the output window
#define EXC_SILENT 0x0008 // do not warn or log to the output window