Currency: Add new forex provider exchangerate.host (#682)

* Add new forex provider ExchangeRateHost.io

* Fix linter paramTypeComine

* Add templates and README files

* Convert all times to UTC

* Fix cosmetic issue and address nits

* Add support for fx exchangerate.host engine override

* Address nit plus use remove plural

cmd/documentation/currency_templates/fx.tmpl

@@ -6,6 +6,7 @@
 + Currency Layer support
 + Fixer.io support
 + Open Exchange Rates support
++ ExchangeRate.host support
 
 ### Please click GoDocs chevron above to view current GoDoc information for this package
 {{template "contributions"}}

cmd/documentation/currency_templates/fx_exchangeratehost.tmpl

@@ -0,0 +1,35 @@
+{{define "currency forexprovider exchangerate.host" -}}
+{{template "header" .}}
+## Current Features for {{.Name}}
+
++ Fetches up to date curency data from [ExchangeRate.host API]("https://exchangerate.host")
+
+### How to enable
+
++ [Enable via configuration](https://github.com/thrasher-corp/gocryptotrader/tree/master/config#enable-currency-via-config-example)
+
++ Individual package example below:
+```go
+import (
+	"github.com/thrasher-corp/gocryptotrader/currency/forexprovider/base"
+	"github.com/thrasher-corp/gocryptotrader/currency/forexprovider/exchangerate.host"
+)
+
+var c exchangeratehost.ExchangeRateHost
+
+// Define configuration
+newSettings := base.Settings{
+	Name:             "ExchangeRateHost",
+	// ...
+}
+
+c.Setup(newSettings)
+
+rates, err := c.GetRates("USD", "EUR,AUD")
+// Handle error
+```
+
+### Please click GoDocs chevron above to view current GoDoc information for this package
+{{template "contributions"}}
+{{template "donations" .}}
+{{- end}}