Add getContractAddressAsync and tests

src/contract_wrappers/exchange_wrapper.ts

@@ -543,6 +543,15 @@ export class ExchangeWrapper extends ContractWrapper {
         logEventObj.watch(callback);
         this._exchangeLogEventObjs.push(logEventObj);
     }
+    /**
+     * Returns the ethereum address of the current exchange contract
+     * on the network that the provided web3 instance is connected to
+     * @return  The ethereum address of the current exchange contract.
+     */
+    public async getContractAddressAsync(): Promise<string> {
+       const exchangeContract = await this._getExchangeContractAsync();
+       return exchangeContract.address;
+    }
     private async _isValidSignatureUsingContractCallAsync(dataHex: string, ecSignature: ECSignature,
                                                           signerAddressHex: string): Promise<boolean> {
         assert.isHexString('dataHex', dataHex);

test/exchange_wrapper_test.ts

@@ -22,6 +22,7 @@ import {
 } from '../src';
 import {FillScenarios} from './utils/fill_scenarios';
 import {TokenUtils} from './utils/token_utils';
+import {assert} from '../src/utils/assert';
 
 chaiSetup.configure();
 const expect = chai.expect;
@@ -709,4 +710,10 @@ describe('ExchangeWrapper', () => {
             expect(orderHash).to.equal(orderHashFromContract);
         });
     });
+    describe('#getContractAddressAsync', () => {
+        it('returns the exchange contract address', async () => {
+            const exchangeAddress = await zeroEx.exchange.getContractAddressAsync();
+            assert.isETHAddressHex('exchangeAddress', exchangeAddress);
+        });
+    });
 });