docs: move protocol-related docs to man section 5

Continue the move of existing Documentation/technical/* protocol and
file-format documentation into our main documentation space. By moving
the things that discuss the protocol we can properly link from
e.g. lsrefs.unborn and protocol.version documentation to a manpage we
build by default.

So far we have been using the "gitformat-" prefix for the
documentation we've been moving over from Documentation/technical/*,
but for protocol documentation let's use "gitprotocol-*".

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refspec.h

@@ -69,7 +69,7 @@ int valid_remote_name(const char *name);
 struct strvec;
 /*
  * Determine what <prefix> values to pass to the peer in ref-prefix lines
- * (see Documentation/technical/protocol-v2.txt).
+ * (see linkgit:gitprotocol-v2[5]).
  */
 void refspec_ref_prefixes(const struct refspec *rs,
 			  struct strvec *ref_prefixes);