Issues related to changed definition of <references>

[reschke]

...as done for #49:

• The grammar describes the <name> child element as optional, but xml2rfc requires it
• Allowing nesting implies that there now can be deeper hierarchies; this needs to be discussed and potentially disallowed in prose
• The <back> element still allows multiple <references> child elements; either the grammar should be restricted or this should be mentioned in prose (this might also require changes in the Style Guide); in particular, a v2 processor will handle two <references> entries in <back> differently than xml2rfv in v3 mode (and that's really confusing)

Proposal: back out the change; it's not needed and was indeed discussed before and rejected. The problem discussed in https://tools.ietf.org/html/draft-levkowetz-xml2rfc-v3-implementation-notes-00#section-3.1.6 could be fixed simply by moving the associated text from the HTML spec to the vocabulary spec.

Potential extension:

• Add "removeInRFC" attribute for references sections that will go away upon RFC publication