Add package and const block comments to imgcache

internal/imgcache/imgcache.go

@@ -1,3 +1,4 @@
+// Package imgcache provides interfaces and types for the image caching proxy.
 package imgcache
 
 import (
@@ -7,9 +8,10 @@ import (
 	"time"
 )
 
-// ImageFormat represents supported output image formats
+// ImageFormat represents supported output image formats.
 type ImageFormat string
 
+// Supported image output formats.
 const (
 	FormatOriginal ImageFormat = "orig"
 	FormatJPEG     ImageFormat = "jpeg"
@@ -30,9 +32,10 @@ func (s Size) OriginalSize() bool {
 	return s.Width == 0 && s.Height == 0
 }
 
-// FitMode represents how to fit image into requested dimensions
+// FitMode represents how to fit image into requested dimensions.
 type FitMode string
 
+// Supported image fit modes.
 const (
 	FitCover   FitMode = "cover"
 	FitContain FitMode = "contain"
@@ -89,9 +92,10 @@ type ImageResponse struct {
 	CacheStatus CacheStatus
 }
 
-// CacheStatus indicates whether the response was served from cache
+// CacheStatus indicates whether the response was served from cache.
 type CacheStatus string
 
+// Cache status values for response headers.
 const (
 	CacheHit   CacheStatus = "HIT"
 	CacheMiss  CacheStatus = "MISS"