Eth2.0-specs: Proposer & Casper Slashing

[decanus]

Currently there are both Proposer and Casper slashings defined. However the difference of the 2 is never explicitly defined. For clarity in the spec this should be done, ideally it would be documented what differentiates the 2 and why this differentiation needs to be made.

[JustinDrake]

• Proposer is about proposers making two distinct proposals on the same shard (the beacon chain counts as a shard for this purpose) in a given epoch.
• Casper is about attesters making two votes that could compromise safety in the context of Casper the Friendly Finality Gadget.

(I'm not a huge fan of "Casper" as a name for various reasons. What about ProposerSlashing and AttesterSlashing?)

[vbuterin]

Yeah, Proposer and Attester is definitely better.

[decanus]

@JustinDrake The name change definitely clarifies it more but we should have those explicit definitions which you've put there in the spec for anyone to easily look over.

[djrtwo]

addressed in #512

Short descriptions can/should be added to helper functions and data structures throughout

[djrtwo]

closed via #512

open new issue if we want to add more descriptions