Consistent handling of evmc_result

[axic]

1. evmc_execute_fn returns it as value
2. evmc_call_fn expects a user specified pointer refering to it, to be filled
3. evmc_release_result_fn expects a pointer to it, yet it

I assume 3. because you wanted it to behave like a C++ destructor.

It would be nice to:

• evmc_call_fn to return the result struct as a value
• evmc_release_result_fn not take a pointer, but a struct

Both these make it even more clear that evmc_result struct cannot be extended by the VM.

[chfast]

I had problems with returning structs with unions in Python so now every host function returning a struct mirrors C ABI. This is actually not so bad because now you can return an error like e.g. in evmc_blockhash().

For evmc_call_fn this could be a good change.
For evmc_release_result_fn it should be a pointer not to copy the whole struct.

[axic]

For evmc_release_result_fn it should be a pointer not to copy the whole struct.

Good point, can you document this reason? Too bad C doesn't have reference syntax, would make this nicer.

Now I wonder if returning a pointer in all cases is better and let release handle it. That we could discuss as a separate thread.