Added benchmark for Commaf

Spoiler: It's kind of slow.  But at least there's some idea how slow
now.
diff --git a/comma_test.go b/comma_test.go
index 1386bd1..49040fb 100644
--- a/comma_test.go
+++ b/comma_test.go
@@ -42,6 +42,7 @@
 		{"1,000", Commaf(1000), "1,000"},
 		{"10,000", Commaf(10000), "10,000"},
 		{"100,000", Commaf(100000), "100,000"},
+		{"834,142.32", Commaf(834142.32), "834,142.32"},
 		{"10,000,000", Commaf(10000000), "10,000,000"},
 		{"10,100,000", Commaf(10100000), "10,100,000"},
 		{"10,010,000", Commaf(10010000), "10,010,000"},
@@ -68,6 +69,12 @@
 	}
 }
 
+func BenchmarkCommaf(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Commaf(1234567890.83584)
+	}
+}
+
 func BenchmarkBigCommas(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		BigComma(big.NewInt(1234567890))