Change version negotation and add ROUTER_KEY null field check.

The lib now downgrade only if the first PDU received contatins a wrong
version number. PDUs received later will be treat as errors.
Add support for new protocol timing parameters.

-If the current session is a version 1 session the timing paramters of the
 EOD PDU will now be used.
- Renamed the old timing value variables to match the terms used in the RFC.