challenge: do challenge 3

* challenge/c03.go: Implement challenge 3
* cryptopals.go (main): Add handling to run challenge 3
* lib/brute.go (XORCrackSingleKey): New function.
* lib/hex.go (HexStrToAsciiStr, ByteToHexStr): New functions.
* lib/str.go (FillStr): New function.

1 files changed, 2 insertions, 0 deletions

diff --git a/cryptopals.go b/cryptopals.go
index 37580be..5faa363 100644
--- a/cryptopals.go
+++ b/cryptopals.go
@@ -22,5 +22,7 @@ func main() {
 		challenge.C1()
 	case 2:
 		challenge.C2()
+	case 3:
+		challenge.C3()
 	}
 }