Move `ipfs repo stat` to `ipfs stats repo`

[RichardLitt]

I think that ipfs repo stat would be more appropriate under the ipfs stats header.

[whyrusleeping]

i think the case could be made to have it be both place, as an alias for the same command

[RichardLitt]

Agreed. Are there other aliases I could look at in the code, to see how to implement a PR myself?

[RichardLitt]

Same goes for:

ipfs bitswap stat
ipfs block stat
ipfs files stat
ipfs object stat