Make the microdesc format a little more flexible, with optional TAP key

[nickm]

Right now we say that a microdesc starts with an onion-key field, and the onion-key contains a 1024-bit RSA key. This is true of any microdesc that we can currently _use_, but for caching purposes, we should probably be more tolerant so that we can have caches tolerate other key types in the distant happy future.

[nickm]

On consideration, giving this one back to 0.2.3.x-final. It's okay to make caches and clients more tolerant once they start fetching anything other than the basic microdesc flavor... and changing the content of the onion-key will want a new flavor anyway.

[nickm]

Actually, this *could* be doable in December, if I can come up with an obviously right and noninvasive way to do it.

[nickm]

I will not finish this by friday, and it would require design.

[nickm]

These go in Tor 0.2.7

[nickm]

Marking triaged-out items from first round of 0.2.7 triage.

[nickm]

Make all non-needs_review, non-needs_revision, 027-triaged-1-out items belong to 0.2.???

[teor]

Milestone renamed

[nickm]

Finally admitting that 0.3.??? was a euphemism for Tor: unspecified all along.

[nickm]

Remove an old triaging keyword.

[nickm]

prop245 needs some revision, but it explains one way to do this.