feat(access): add AccessControl

Cargo.toml

@@ -8,6 +8,7 @@ members = [
   "examples/erc721",
   "examples/merkle-proofs",
   "examples/ownable",
+  "examples/access-control",
 ]
 # Explicitly set the resolver to version 2, which is the default for packages
 # with edition >= 2021.

contracts/Cargo.toml

@@ -37,6 +37,7 @@ erc721_metadata = ["erc721"]
 
 access = []
 ownable = ["access"]
+control = ["access"]
 
 # Enables using the standard library. This is not included in the default
 # features, because this crate is meant to be used in a `no_std` environment.