add option to filter by file identifier

[rerpha]

So i can do saluki listen localhost:9092/sometopic --filter f144 to only see f144 messages etc.

[rerpha]

for now just do this for listen, consume requires a bit of thought as -m may not even include any messages of that particular file ID, should -m x --filter y just show last x messages of file ID y or just discard x messages where file id is not y?

[rerpha]

done in #37