Python gen: allow for hex and binary notation in enum value attributes

Problem: specifying long ints in base 10 format can get verbose/confusing, for example when setting up a 32-bit bitmask (eg. for heartbeat->custom_mode).  And unfortunately using shift operator (eg. 1<<31) is not practical due to XML syntax.  Using hex or binary can be much more readable in some cases.  Also, the previous constraint of unsignedShort was too short :)

Here is a quick solution. 

Thanks,
-Max