RFC Request: Index number to refer to datasets

[dustmop]

When we run qri list, we get output like this:

1  b6/PLUTO_manhattan
    /ipfs/Qmb4JwhS6iMHatFuZcTFR7C6p5nRkxwmnJdDFfSSihmZYW
    12 MBs, 42966 entries, 0 errors
2  b6/qri_growth
    /ipfs/QmRW74zHw2pdmDnmASDirjxztxDj5B5FdXCjZ9ApyTD2to
    Qri Growth Stats
    Using Qri to track the growth of Qri
    660 bytes, 1 entries, 0 errors

The numbers on the left-most column (1 and 2) should be usable to refer to these datasets. So I could run qri get 1 to get information about b6/PLUTO_manhattan. Implementing this requires:

• having a guarantee that the order of qri list is deterministic over short-term periods. I think this is true right now; it's just the order of the contents of ~/.qri/peers.json
• having a usable syntax to use index numbers. Datasets can't start with numerals, so I believe using the numbers alone should be okay?

This feature resembles git's stash command, which outputs indexed names for stashes when listing, that can be used to refer to stashes in future commands.