Spec - 2.1 - Add support for the mirrors role

[heartsucker]

[trishankkarthik]

Fortunately, this has so far been an optional, and the least important role in TUF :) I think the map file should be able to completely replace this role... @JustinCappos

[heartsucker]

@trishankkarthik Yes, this is true. Someone I know in SF wanted to help out, so I started making some basic tickets that for now would let others contribute without me stepping all over them.

[trishankkarthik]

Thanks for all your efforts! Looking forward...