revid-cli: sensible defaults and option values depending on the output mode.

[Alan Noble]

For example, the default packetization for HTTP should be Mpegts, whereas for RTMP it should be Flv.

The ring buffer size should also be smaller for HTTP (say 100) than for RTMP (say 1000).

Similarly, the ring buffer element size should be tuned for the payload type.

There may be other parameters that can be tuned as well .

[Saxon Milton]

Resolved in PR #153