Merge PR cosmos#2990: Update f1 spec

* Update f1 spec:

* Improves exposition of the base scheme
* Fix inflation section / add sketch of how to do it
* Add future work section

I've also realized that using the ideas of the inflation section,
we could even remove the iteration over slashes when withdrawing!
(Note, inflation section equations / proof of correctness has not been
thoroughly transcribed from my head onto paper, so its not guaranteed to
be correct at the moment. However the inflation section of this describes
something separate from inflation in the hub. It has inflation happen by
having each staked token produce more staked tokens, instead of having it come
through block rewards. This inflation can also happen per validator,
so as to enable non-signing validators to not get inflation)

* Fix grammar

Co-Authored-By: ValarDragon <[email protected]>

* Add proof of correctness to the inflation section

* Re-update PDF after merging chris' fixes

* address more of @cwgoes' suggestions