suggestion！export more infomation for checking method in one place， give avalable message after message executed

[hunjixin]

1. It would be better to export a struct include method function and some extra filed like below

type ActorMethod struct {
	MethodFunc interface{}
	ImmediateCaller   addr.Address
	CallerType    []cid.Cid
	AccessRole   int
	//  ... etc
}

In this way, we can control all method check in the same code, instead of writing sanity-checking code in every method once

2. noticed that the return value of the publishstoragedeals method has become null.

// this project
func (a *StorageMarketActor) PublishStorageDeals(rt Runtime, params *PublishStorageDealsParams) *adt.EmptyValue {

//lotus
func (sma StorageMarketActor) PublishStorageDeals(act *types.Actor, vmctx types.VMContext, params *PublishStorageDealsParams) ([]byte, ActorError) {

hope some methods can give some valuable information instead of becoming adt.emptyvalue

[anorth]

I interpret the first request as talking about a declarative form for caller and other validation, as opposed to the current procedural form.

I agree that would have some benefits. I'm marking this non-urgent for now. We should be able to improve this later without breaking compatibility (unless it reveals bugs).

[anorth]

Folding in to #178.