Buflines need to know which part of text to wrap with the timestamp. The
second parameter to `AddLine` (and shorthands) is that text, which after
wrapping is added as the `text` parameter to `NamedFormat`.
Timestamps are formatted at the moment buffers are flushed to the
client. The client parameter to `GetLine` provides access to the User
and the new server-time capability.
This is in preparation of adding more attributes to a CBufLine. Going
forward, at least savebuf will need access to all of these to properly
serialize buffers.
Basically, instead of relying on `GetLine()` to return `false`, the
caller is now expected to check bounds himself using `Size()`.
