EP Native Orders (#27)

* `@0x/contracts-zero-ex`: add limit orders feature
`@0x/contracts-utils`: add `uint128` functions to `LibSafeMathV06`

* `@0x/contract-addresses`: Update ganache snapshot addresses

* `@0x/contracts-zero-ex`: Mask EIP712 struct hash values.

* `@0x/contracts-zero-ex`: Add more limit order tests

* `@0x/contracts-zero-ex`: Fix typos

* `@0x/contracts-zero-ex`: Compute fee collector address after protocol fee zero check.

* `@0x/contracts-zero-ex`: Remove WETH payment logic from fee collector fixin

* `@0x/contracts-zero-ex`: Convert all ETH to WETH in `FeeCollector`.

* `@0x/contracts-zero-ex`: Address review feedback

* `@0x/contracts-zero-ex`: Export more utils

* `@0x/contracts-zero-ex`: Rename `LimitOrdersFeatures`, `LibLimitOrders`, etc. into `*NativeOrders*`.
`@0x/contracts-zero-ex`: Emit `protocolFeePaid` in native order fill events.
`@0x/contracts-zero-ex`: Refactor to get around stack limits.
`@0x/contracts-zero-ex`: Use different storage mappings for RFQ and limit order pair cancellations.

* `@0x/contracts-zero-ex`: Add `getProtocolFeeMultiplier()` and `transferProtocolFeesForPools()` to `NativeOrdersFeature`.

* `@0x/contracts-zero-ex`: Fix broken tests

* update orders docs

* `@0x/contracts-zero-ex`: Add more tests to `NativeOrdersFeature`

* rebuild after rebase

* `@0x/contract-addresses`: Fix changelog booboo

* `@0x/contracts-zero-ex`: Add method selectors output to generated artifacts

* `@0x/contracts-zero-ex`: Add maker address to order cancel events.
`@0x/contracts-zreo-ex`: Remove `UpTo` suffix from order pair cancellation functions.
`@0x/contracts-zreo-ex`: Address misc review comments.

* `@0x/contracts-zero-ex`: More SafeMath in native orders

* update orders docs

Co-authored-by: Lawrence Forman <me@merklejerk.com>

contracts/zero-ex/test/utils/orders.ts

@@ -0,0 +1,43 @@
+import { getRandomInteger, randomAddress } from '@0x/contracts-test-utils';
+import { BigNumber, hexUtils } from '@0x/utils';
+
+import { LimitOrder, LimitOrderFields, RfqOrder, RfqOrderFields } from '../../src/orders';
+
+/**
+ * Generate a random limit order.
+ */
+export function getRandomLimitOrder(fields: Partial<LimitOrderFields> = {}): LimitOrder {
+    return new LimitOrder({
+        makerToken: randomAddress(),
+        takerToken: randomAddress(),
+        makerAmount: getRandomInteger('1e18', '100e18'),
+        takerAmount: getRandomInteger('1e6', '100e6'),
+        takerTokenFeeAmount: getRandomInteger('0.01e18', '1e18'),
+        maker: randomAddress(),
+        taker: randomAddress(),
+        sender: randomAddress(),
+        feeRecipient: randomAddress(),
+        pool: hexUtils.random(),
+        expiry: new BigNumber(Math.floor(Date.now() / 1000 + 60)),
+        salt: new BigNumber(hexUtils.random()),
+        ...fields,
+    });
+}
+
+/**
+ * Generate a random RFQ order.
+ */
+export function getRandomRfqOrder(fields: Partial<RfqOrderFields> = {}): RfqOrder {
+    return new RfqOrder({
+        makerToken: randomAddress(),
+        takerToken: randomAddress(),
+        makerAmount: getRandomInteger('1e18', '100e18'),
+        takerAmount: getRandomInteger('1e6', '100e6'),
+        maker: randomAddress(),
+        txOrigin: randomAddress(),
+        pool: hexUtils.random(),
+        expiry: new BigNumber(Math.floor(Date.now() / 1000 + 60)),
+        salt: new BigNumber(hexUtils.random()),
+        ...fields,
+    });
+}