Begin private voting docs

[ValarDragon]

Starting some documentation for how I suggest architecting private voting into the DAO DAO design.

This is very WIP. If I get more time available during the week, will write up more on circuit design / other constraints!

Rendered readme - gives higher level overview, and where its expected to sit in with other modules

Rendered Spec - Intended to go into more details of cryptographic constructions, merkle trees involved, and client side UX. Still have a ways to go on this unfortunately

Code - Not started yet

[0xekez]

this is really cool. i like your description of zcash and the idea here. it sounds reasonably intuitive, though i'm unfamiliar with zk proofs so i'm unable to verify it. :)

one note from reading through:

So the voting power a shielded voter has, must either be frozen at proposal start time..

we do all of our voting power as a function of block height so that this is the case. from your earlier interface, this makes it:

pub trait VoteModule {
  fn voting_power_by_addr(&self, addr: Addr, height: u64) -> Option<Uint128>
}

allowing voting powers to decrease may be fine though, so long as we don't also allow increases.