add `dig` and `bury` options

[rerpha]

To dump/resend data from a topic and from a dump respectively.

    # saluki bury - dump data on topic to file
    # saluki bury mybroker:9092/topicname -o startoffset finishoffset outputfile
    # saluki bury mybroker:9092/topicname -t starttimestamp finishtimestamp outputfile

    # saluki dig - push data from dump generated by saluki bury to topic
    # saluki dig mybroker:9092/topicname outputfile

for this to work we need to store the data in a dump file and be opinionated about it's format.
we probably need to store:

• key
• value
• timestamp
• partition
  (anything else?)
  so an appropriate format needs to get written and parsed by the respective commands.