Create a struct with all of Hugo's config options

Primary motivation is documentation, but it will also hopefully simplify the code.

Also,

* Lower case the default output format names; this is in line with the custom ones (map keys) and how
it's treated all the places. This avoids doing `stringds.EqualFold` everywhere.

Closes #10896
Closes #10620

common/htime/time.go

@@ -14,6 +14,7 @@
 package htime
 
 import (
+	"log"
 	"strings"
 	"time"
 
@@ -163,3 +164,11 @@ func Since(t time.Time) time.Duration {
 type AsTimeProvider interface {
 	AsTime(zone *time.Location) time.Time
 }
+
+// StopWatch is a simple helper to measure time during development.
+func StopWatch(name string) func() {
+	start := time.Now()
+	return func() {
+		log.Printf("StopWatch %q took %s", name, time.Since(start))
+	}
+}