Add US unit support for weather observations and forecasts

internal/core/constants.go

@@ -0,0 +1,19 @@
+package core
+
+// Units controls response-unit output formatting.
+type Units string
+
+const (
+	UnitsMetric Units = "metric"
+	UnitsUS     Units = "us"
+)
+
+const (
+	celsiusToFahrenheitScale  = 9.0 / 5.0
+	celsiusToFahrenheitOffset = 32.0
+	kmhToMphFactor            = 0.621371192237334
+	metersToMilesFactor       = 0.000621371192237334
+	metersToFeetFactor        = 3.280839895013123
+	paToInHgFactor            = 0.000295299830714045
+	mmToInchesFactor          = 0.03937007874015748
+)