Support itbit exchange/ticker. Additions (#232)

* Initial itBit implementation

* Add tests for calculatePrice in exchange/itbit.js

* Add etherium to supported crypto codes in common/itbit.js

* Apply standardjs to itbit files

* itbit trade test. not important

* test getCurrencyRates in ticker/itbit.js

lib/plugins/exchange/itbit/itbit.js

@@ -0,0 +1,45 @@
+const common = require('../../common/itbit')
+const coinUtils = require('../../../coin-utils')
+
+exports.buy = function (account, cryptoAtoms, fiatCode, cryptoCode) {
+  return trade('buy', account, cryptoAtoms, fiatCode, cryptoCode)
+}
+
+exports.sell = function (account, cryptoAtoms, fiatCode, cryptoCode) {
+  return trade('sell', account, cryptoAtoms, fiatCode, cryptoCode)
+}
+
+function trade (type, account, cryptoAtoms, fiatCode, cryptoCode) {
+  try {
+    const instrument = common.buildMarket(fiatCode, cryptoCode)
+    const cryptoAmount = coinUtils.toUnit(cryptoAtoms, cryptoCode)
+
+    return calculatePrice(type, instrument, cryptoAmount)
+      .then(price => {
+        const args = {
+          side: type,
+          type: 'limit',
+          currency: cryptoCode,
+          amount: cryptoAmount.toFixed(4),
+          price: price.toFixed(2),
+          instrument: instrument
+        }
+        return common.authRequest(account, 'POST', '/wallets/' + account.walletId + '/orders', args)
+      })
+  } catch (e) {
+    return Promise.reject(e)
+  }
+}
+
+function calculatePrice (type, tickerSymbol, amount) {
+  return common.request('GET', '/markets/' + tickerSymbol + '/order_book')
+    .then(orderBook => {
+      const book = type == 'buy' ? 'asks' : 'bids'
+      let collected = 0.0
+      for (const entry of orderBook[book]) {
+        collected += parseFloat(entry[1])
+        if (collected >= amount) return parseFloat(entry[0])
+      }
+      throw new Error('Insufficient market depth')
+    })
+}