Protocol documentation fix

[thierry-f-78]

Hi,

I'm currently regarding to implement RELP server. I'm processing offer message.

I see in the doc this definition of offer message:

OFFER = LF FEATURENAME ["=" VALUE *("," VALUE)]

But, I do not constat this format in practice with rsyslog client. It seems the LF char is added at the end of message only if it is not the last message.

https://github.com/rsyslog/librelp/blob/master/src/offers.c#L355

I suggest to update doc like this:

OFFERLIST = OFFER *( LF OFFER )
OFFER = FEATURENAME ["=" VALUE *("," VALUE)]

According with doc, at least one offer is mandatory (relp_version) so the ABNF below describe this.

Thierry