SS58 Address

[JoshOrndorff]

My attempt at revising the address format docs from the parity wiki. (see issue #90)

Sources:
Ss58Codec implementation https://github.com/paritytech/substrate/blob/cf4a28a7e707190c44e73451e9da38de6bb160ec/core/primitives/src/crypto.rs#L235-L285

ss58hash function https://github.com/paritytech/substrate/blob/cf4a28a7e707190c44e73451e9da38de6bb160ec/core/primitives/src/crypto.rs#L224-L232

PR of most recent overhaul paritytech/substrate#1795

[JoshOrndorff]

Thanks for the fixes Joe!
I've fixed the last todo item as well.

I wouldn't mind someone checking this for correctness, but I'm confident enough that I'm willing to merge it if nobody has time to dig in. Might not be too hard to fact check by following the links above.

The merge conflict is a silly mistake I keep making because I forget to build before pushing which means the translation stuff doesn't get updated. I'll be able to easily resolve it.