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/ticker/itbit/itbit.js

@@ -0,0 +1,54 @@
+const axios = require('axios')
+const _ = require('lodash/fp')
+
+const BN = require('../../../bn')
+const common = require('../../common/itbit')
+
+exports.NAME = 'itBit'
+exports.SUPPORTED_MODULES = ['ticker']
+
+function findCurrency (fxRates, fiatCode) {
+  const rates = _.find(_.matchesProperty('code', fiatCode), fxRates)
+  if (!rates || !rates.rate) throw new Error(`Unsupported currency: ${fiatCode}`)
+  return BN(rates.rate)
+}
+
+exports.ticker = function ticker (account, fiatCode, cryptoCode) {
+  if (_.includes(fiatCode, ['USD', 'EUR', 'SGD'])) {
+    return getCurrencyRates(fiatCode, cryptoCode)
+  }
+
+  return axios.get('https://bitpay.com/api/rates')
+    .then(response => {
+      const fxRates = response.data
+      try {
+        const usdRate = findCurrency(fxRates, 'USD')
+        const fxRate = findCurrency(fxRates, fiatCode).div(usdRate)
+
+        return getCurrencyRates('USD', cryptoCode)
+          .then(res => ({
+            rates: {
+              ask: res.rates.ask.times(fxRate),
+              bid: res.rates.bid.times(fxRate)
+            }
+          }))
+      } catch (e) {
+        return Promise.reject(e)
+      }
+    })
+}
+
+function getCurrencyRates (fiatCode, cryptoCode) {
+  try {
+    const market = common.buildMarket(fiatCode, cryptoCode)
+    return common.request('GET', '/markets/' + market + '/ticker')
+      .then(r => ({
+        rates: {
+          ask: BN(r.ask),
+          bid: BN(r.bid)
+        }
+      }))
+  } catch (e) {
+    return Promise.reject(e)
+  }
+}