reader: add Configure() method to configure a reader

takes a key as string and value as interface and attempts
to coerce the value into the appropriate format/type
based on the specified key.
reader: eliminate busy loop when draining finishedMessages
reader: fix Touch deadlock; fix Requeue
Merge pull request #17 from mreiferson/commands_17

reader: fix msg.Requeue and potential msg.Touch deadlock
Merge pull request #16 from mreiferson/busy_loop_16

reader: busy loop while draining
Merge pull request #14 from mreiferson/config_14

reader: add Configure()
bump 0.3.4-alpha