Add pendingmatch flag to orderbook query response

[EnderCrypto]

Description

Prevent cross order
Meanwhile, need merge https://github.com/binance-chain/http-ap/pull/85 and bnb-chain/go-sdk#110 with this change

Rationale

Here is an example of crossed price levels in websocket depth:
After BeginBlock of height 101, the round order (sell, price=3,quantity=5) was inserted into order book. Websocket queried node depth API and the response included this order. and then an order (buy price=3,quantity=9) was also inserted into order book. After matching, in the endblock the remaining price level (buy, price=3,quantity=4) was published to websocket as delta. However, the price level (sell, price=3,quantity=5) still stayed in websocket depth cache, hence the crossed order (buy, 3,5) and (sell, 3,4) received by websocket subscriber. The price level (buy, 3,5) actually doesn’t exist in the real order book.

Solution:

Add a boolean flag “pending_match” in node depth API response to indicate the case of unmatched round orders in order book.
If len(roundOrders[symbol])>0, “pending_match” = true. The drawback is for mini-tokens, the roundOrders will be kept for several blocks until match, and hence the client has a lower chance to get order book with pending_match=false.

The client (websocket-ap) will discard this query result when pendingMatch is true.

Example

RUN TestGetDepth
{"Height":2644,"Levels":[{"buyQty":"0.00000000","buyPrice":"0.00000000","sellQty":"0.00000000","sellPrice":"0.00000000"},{"buyQty":"0.00000000","buyPrice":"0.00000000","sellQty":"0.00000000","sellPrice":"0.00000000"}],"PendingMatch":true}

Changes

Notable changes:

• Add a bool flag pending_match in orderbook API

Preflight checks

• build passed (make build)
• tests passed (make test)
• integration tests passed (make integration_test)
• manual transaction test passed (cli invoke)

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