tpl: Use xxHash instead of MD5 to hash the deferred templates

Motivation is performance. These templates are typically very small, so the win is minor, I guess.

helpers/general.go

@@ -27,6 +27,7 @@ import (
 	"unicode"
 	"unicode/utf8"
 
+	"github.com/cespare/xxhash/v2"
 	"github.com/spf13/afero"
 
 	"github.com/jdkato/prose/transform"
@@ -257,6 +258,14 @@ func SliceToLower(s []string) []string {
 	return l
 }
 
+// XxHashString takes a string and returns its xxHash hash.
+func XxHashString(f string) string {
+	h := xxhash.New()
+	h.WriteString(f)
+	hash := h.Sum(nil)
+	return hex.EncodeToString(hash)
+}
+
 // MD5String takes a string and returns its MD5 hash.
 func MD5String(f string) string {
 	h := md5.New()

tpl/tplimpl/template_ast_transformers.go

@@ -254,7 +254,7 @@ func (c *templateContext) handleDefer(withNode *parse.WithNode) {
 		c.err = errors.New("resources.PostProcess cannot be used in a deferred template")
 		return
 	}
-	innerHash := helpers.MD5String(s)
+	innerHash := helpers.XxHashString(s)
 	deferredID := tpl.HugoDeferredTemplatePrefix + innerHash
 
 	c.deferNodes[deferredID] = inner