(Small) progress on ABNF conversion (issue 36)

Hi,

I've decided to make some more steps towards using the RFC5234 ABNF 
syntax (see issue <http://trac.tools.ietf.org/wg/httpbis/trac/ticket/36>):

1) Use "/" instead of "|" (mainly to silence those people that keep 
pointing out that we use an obsolete notation), see 
<http://trac.tools.ietf.org/wg/httpbis/trac/changeset/334>, and

2) Reference RFC5234 instead of RFC822, and just point out the 
differences that are left (being the list rule and implied LWS); in 
particular do not repeat the other ABNF rules anymore; see 
<http://trac.tools.ietf.org/wg/httpbis/trac/changeset/335>

As far as I recall, the core rules that we use are already aligned with 
RFC5234 (Appendix B.1); should we get rid of them (in 
<http://greenbytes.de/tech/webdav/draft-ietf-httpbis-p1-messaging-latest.html#rfc.section.2.2>)?

Feedback appreciated,

Julian