Add types for accountInfo, order, prices & time

[bennycode]

Here is my PR with an initial definition for the methods accountInfo, order, prices & time to kick-off TypeScript support. To make sure that the definitions are correct, I checked original payload responses as well as the official Rest API for Binance (2017-12-01).

To be consistent with other Binance APIs, I synchronized the naming of the defined types with Binance's Java API:

• Account.java
• AssetBalance.java
• NewOrder.java
• Order.java
• OrderSide.java
• OrderStatus.java
• OrderType.java
• TimeInForce.java

The only thing were I have been unsure are the parameters used for price, stopPrice and icebergQty. The documentation here says that these are numbers (https://github.com/HyperCubeProject/binance-api-node#authenticated-rest-endpoints) but all other clients treat them as strings. I also guess these should be strings?

Here is an example on how this library can now be used with TypeScript:

import Binance, {Account, AssetBalance} from 'binance-api-node';

const client = Binance({
  apiKey: '...',
  apiSecret: '...',
});

client.accountInfo().then((info: Account) => {
  const balances: Array<AssetBalance> = info.balances;
  console.log(`Your account trades ${balances.length} assets.`);
});

Best from Berlin,
Benny

[coveralls]

Coverage decreased (-17.6%) to 75.676% when pulling 1cf300f on bennyn:type-definitions into 6c1607b on HyperCubeProject:master.

[balthazar]

This looks really good, thanks! Yeah I'm quite unsure about the price and stopPrice, this is what the binance docs were saying that I followed. Maybe even passing a sting is fine since they might do the casting on their side too. Merging!