logproto: Added suffix based multiline mode.

Suffix-based multiline is very similar to prefix-garbage based, except it
appends the garbage part to the message as well. With this way, the user can
workaround the absence of multi-line timeout feature.

The only difference in config that the user should use
multi-line-mode(regexp-suffix) in the config. multi-line-prefix() and
multi-line-garbage() options remained the same.

Requested-by: Evan Rempel <erempel@uvic.ca>
Signed-off-by: Tusa Viktor <tusavik@gmail.com>