Fixed trap segfaults & memory management

 - TrapSession, for V1 traps at least, is now reliable
   + Free of segfaults & memory leaks
 - TrapHandler may still have memory management issues
   + Running the session example, sending 100_000 traps, the memory is
   constant for the session, but the trap_handler slowly rizes
   + TrapHandler is not freeing pdu's correctly, and segfaults when I try
   + The memory climb is slow... but for a long lived application could be
   a problem
 - Had to hack the memory management for V1 traps, freeing the enterprise
   oid manually. Can't figure out why it doesn't work... adding logging to
   the native libraries I can see the correct address is being freed.
   Still, for some reason, it fails intermittently. So, I'm freeing this
   OID and setting it to null before calling `snmp_free_pdu` in `PDU.free`
NOTE: Need to fix v1 trap test
Segfaults for TrapHandler & TrapReceiver fixed
Fixed v1 & v2 trap specs
Adding TODO.md file
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