FIP-0045: update to match deployed types

[rvagg]

Background: it was discovered (by @LexLuthr) that ClaimExtensionRequest has been implemented wrong in go-state-types so has not been a functional API on the network since nv10, although it was launched (as per this FIP) in nv9 with the types matching. That's being rectified in filecoin-project/go-state-types#254, although it's conforming to the implementation found in builtin-actors rather than the text of the spec in this FIP.

In the process of proposing a retroactive fix to this spec to match the deployed implementation, I've discovered that there are a lot more mismatched types between spec and implementation, so I've adjusted them all here. This isn't a new FIP, but rather an alignment of the spec if we view the spec as a combination of the FIP text and the builtin-actors implementation; and the only thing changing in code as a result of this is a fix to make ClaimExtensionRequest work.

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• Many of the type fields marked as Address in here were launched in nv9 as ActorID.
• AllocationRequest and ClaimExtensionRequest went live in nv9 with provider as Address but in nv10 switched to ActorID.
• ClaimExtensionRequest was never adjusted in go-state-types to ActorID so has been unable to successfully parse or pass on these to builtin-actors. ExtendClaimTerms appears to have been the only mechanism used to extend claim terms since this FIP.
• Minor: updated all epoch fields to match within this FIP, I chose to use int64 which is the base type used in implementations.
• Add missing docs for AllocationRequest and ClaimExtensionRequest fields.
• Added historical notes section.

[rvagg]

Thanks to Aayush for pointing out that I was using builtin-actor versions instead of network versions. I've fixed that now, 9->17 and 10->18.