Aligned the "Minute" members of intraday and historical data points.

They appear to both be used the same way, as a string field that tells
us the minute of the data point in the time zone of the exchange.

I also removed, rather than update, a helper function that attempts to get the time from the
historical data point by combining the date and minute fields. The
problem is that this results in the wrong time because the time objects
are in UTC, so to do this right you'd need to know the time zone which
the "minute" value is in. I think we should leave it up to the consumer
to write their methods to convert times according to their special
circumstances.

client_test.go

@@ -498,6 +498,7 @@ func TestHistoricalPrices(t *testing.T) {
 					"key": "AAPL",
 					"subkey": "12345",
 					"date": "2021-12-03",
+					"minute": "9:30",
 					"uOpen": 164.02,
 					"uClose": 161.84,
 					"uHigh": 164.96,
@@ -521,6 +522,7 @@ func TestHistoricalPrices(t *testing.T) {
 				Key:            "AAPL",
 				Subkey:         "12345",
 				Date:           Date(time.Date(2021, 12, 3, 0, 0, 0, 0, time.UTC)),
+				Minute:         HourMinute(9*time.Hour + 30*time.Minute),
 				UOpen:          164.02,
 				UClose:         161.84,
 				UHigh:          164.96,

historical.go

@@ -6,7 +6,6 @@
 package iex
 
 import (
-	"fmt"
 	"time"
 )
 
@@ -112,39 +111,26 @@ type IntradayHistoricalOptions struct {
 
 // HistoricalDataPoint Represents a single historical data point for a stock
 type HistoricalDataPoint struct {
-	Close          float64 `json:"close"`
-	High           float64 `json:"high"`
-	Low            float64 `json:"low"`
-	Open           float64 `json:"open"`
-	Symbol         string  `json:"symbol"`
-	Volume         float64 `json:"volume"`
-	ID             string  `json:"id"`
-	Key            string  `json:"key"`
-	Subkey         string  `json:"subkey"`
-	Date           Date    `json:"date"`
-	Minute         string  `json:"minute"`
-	UOpen          float64 `json:"uOpen"`
-	UClose         float64 `json:"uClose"`
-	UHigh          float64 `json:"uHigh"`
-	ULow           float64 `json:"uLow"`
-	UVolume        int     `json:"uVolume"`
-	Change         float64 `json:"change"`
-	ChangePercent  float64 `json:"changePercent"`
-	Label          string  `json:"label"`
-	ChangeOverTime float64 `json:"changeOverTime"`
-}
-
-// Time merges HistoricalDataPoint's Date and Mintue field and
-// get the exact time. Useful for "5dm" and "1mm" time frames
-func (p HistoricalDataPoint) Time() time.Time {
-	if p.Minute == "" {
-		return time.Time(p.Date)
-	}
-
-	layout := "2006-01-02 15:04"
-	dateStr := fmt.Sprintf("%s %s", p.Date.String(), p.Minute)
-	t, _ := time.Parse(layout, dateStr)
-	return t
+	Close          float64    `json:"close"`
+	High           float64    `json:"high"`
+	Low            float64    `json:"low"`
+	Open           float64    `json:"open"`
+	Symbol         string     `json:"symbol"`
+	Volume         float64    `json:"volume"`
+	ID             string     `json:"id"`
+	Key            string     `json:"key"`
+	Subkey         string     `json:"subkey"`
+	Date           Date       `json:"date"`
+	Minute         HourMinute `json:"minute"`
+	UOpen          float64    `json:"uOpen"`
+	UClose         float64    `json:"uClose"`
+	UHigh          float64    `json:"uHigh"`
+	ULow           float64    `json:"uLow"`
+	UVolume        int        `json:"uVolume"`
+	Change         float64    `json:"change"`
+	ChangePercent  float64    `json:"changePercent"`
+	Label          string     `json:"label"`
+	ChangeOverTime float64    `json:"changeOverTime"`
 }
 
 // IntradayOptions optional query params to pass to intraday endpoint