add `dig` and `bury` options

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.