EIP-001: Specify the calling convention and memory lookup for plugin IO

[nilslice]

@zshipko, I've set up a EIP-001 doc in main to work off of for this spec!

[zshipko]

I added some initial ideas after our discussion, I will probably make some changes next week but it's been updated some thoughts about the direction we could take it in.

[nilslice]

That looks great! After looking through usage of the Table API, it seemed like maybe we were going to have to force it a bit and comparatively, the Global API seems to be more fitting.

I think it would be possible to hide the details of any mutable global from the plugin author, since they would only be calling wrapped external functions for the offset/length calls. But from the examples in the Global docs, I'm not certain... namely the linking done to provide access to the values within the module from the host.