FIL VM Runtime Interface Update

[yiannisbot]

This PR updates the specification for the FIL VM Runtime Interface & Exit codes.

I have excluded mention to the vm/implementation and code loading, as I found these parts too implementation-specific and therefore, not belonging to this spec. Let me know if we want to do otherwise and if so, which are the important points from those parts that we should be referring to.

[anorth]

I object to duplicating all this code and prose from the specs-actors repo. That repo is the spec, it was broken out from this one precisely to avoid the maintenance nightmare that will arise from having two versions of this, only one of which (the executable code) stands a chance of being correct.

Please link to the specs-actors repo instead. To the extent that prose can be improved, please do so with PRs to the specs-actors repo.

[yiannisbot]

@anorth I've removed all redundant text and code and pointed to the respective repositories. Let me know if there's some part of the code that needs a special mention or description in text, so that I work to include it.

[yiannisbot]

@hugomrdias this is ready to merge.

[hugomrdias]

still targeting beta

The base branch was changed.

[hugomrdias]

you didnt change the links yet

[yiannisbot]

@hugomrdias I did now :)