many many cleanups

- remove inelegant ProtocolWrapper class
- use twisted Deferreds more appropriately
- better disconnection/termination behavior
- saner compatibility with multiple reader connections
simplify reset & inventory scripts

notably, allow multiple hostnames on the command line
saner presentation of Failure messages
add LLRPMessage.isSuccess()

indicates whether an LLRP message contains a "success" status message, which is
unfortunately not represented consistently in the various response messages
convenience class methods for state machine representation
restructure state machine in terms of Twisted defer.Deferred

this allows for many API simplifications
catch malformed READER_EVENT_NOTIFICATION
fix tests
factor out arg parsing and log init
remove superfluous ReaderThread
remove threading

everything goes through the reactor
beta warning in readme