add 165 to 721 (#972)

* make _tokenId indexed in Transfer and Approval events

via: https://github.com/ethereum/EIPs/pull/1124/files

* fix: make name() and symbol() external instead of public

* feat: implement ERC721's ERC165

* feat: erc165 tests

* fix: don't use chai-as-promised in direct await

* fix: reorganize to /introspection

* feat: abstract all erc165 tests to a behavior

* feat: disallow registering 0xffffffff

test/helpers/makeInterfaceId.js

@@ -0,0 +1,21 @@
+import { soliditySha3 } from 'web3-utils';
+
+const INTERFACE_ID_LENGTH = 4;
+
+export default (interfaces = []) => {
+  const interfaceIdBuffer = interfaces
+    .map(methodSignature => soliditySha3(methodSignature)) // keccak256
+    .map(h =>
+      Buffer
+        .from(h.substring(2), 'hex')
+        .slice(0, 4) // bytes4()
+    )
+    .reduce((memo, bytes) => {
+      for (let i = 0; i < INTERFACE_ID_LENGTH; i++) {
+        memo[i] = memo[i] ^ bytes[i]; // xor
+      }
+      return memo;
+    }, Buffer.alloc(INTERFACE_ID_LENGTH));
+
+  return `0x${interfaceIdBuffer.toString('hex')}`;
+};