Refactor out the use of rice in favor of embed (#2)

Co-authored-by: James Mills <prologic@shortcircuit.net.au>
Reviewed-on: https://git.mills.io/prologic/spyda/pulls/2

internal/templates/templates.go

@@ -0,0 +1,22 @@
+package templates
+
+import (
+	"embed"
+	"io/fs"
+)
+
+//go:embed *.html
+var templates embed.FS
+
+// MustGetTemplate returns a template string with the given name.
+func MustGetTemplate(name string) string {
+	b, err := templates.ReadFile(name)
+	if err != nil {
+		panic(err)
+	}
+	return string(b)
+}
+
+func FS() fs.FS {
+	return templates
+}