Move references to informational references

[ianswett]

Moves references to informational references, clarifies that SRTT and RTTVar are computed based on an RFC, and adds todos for the congestion control section for anything formerly in the references section.

[MikeBishop]

BTW, if they're not referenced in the text, why do they need to be in the references?

[ianswett]

All of these were informational for me when implementing QUIC, so I felt they should be included. I believe most of them should be referenced in the text, so I'll try to make sure as many as possible are referenced in an updated version of this PR.

[ianswett]

I just reviewed the references that aren't currently in the text, and they're all congestion control related, which is the next section that I plan to properly document, so they should be referenced soon.

[MikeBishop]

Great -- if they're referenced as {{?RFCXXXX}}, you don't need to (and perhaps can't?) have them explicitly in the refs at the top, so remove them from there as you add the inline references.  Or you can reference things that are explicitly in the references as [RFCXXXX] instead.