Add last night's progress.

Basic functionality for HOTP, TOTP, and YubiKey OTP. Still need YubiKey
HMAC, serialisation, check, and scan.

modhex/example_test.go

@@ -0,0 +1,29 @@
+package modhex
+
+import (
+	"fmt"
+	"github.com/gokyle/twofactor/modhex"
+)
+
+var out = "fjhghrhrhvdrdciihvidhrhfdb"
+var in = "Hello, world!"
+
+func ExampleEncoding_EncodeToString() {
+	data := []byte("Hello, world!")
+	str := modhex.StdEncoding.EncodeToString(data)
+	fmt.Println(str)
+	// Output:
+	// fjhghrhrhvdrdciihvidhrhfdb
+}
+
+func ExampleEncoding_DecodeString() {
+	str := "fjhghrhrhvdrdciihvidhrhfdb"
+	data, err := modhex.StdEncoding.DecodeString(str)
+	if err != nil {
+		fmt.Printf("%v\n", err)
+		return
+	}
+	fmt.Printf("%s", string(data))
+	// Output:
+	// Hello, world!
+}