Added Cryptopals Crypto Challenges resource (#35)

* Added Cryptopals Crypto Challenges resource

* Removed broken resource

- Fixes #34

* Ordered resources in alphabetical order

README.md

@@ -336,7 +336,6 @@ encryption library providing MD5, SHA1, SHA2 hashing and HMAC functionality, as
 
 ### Web-tools
 
-- [Crypo](http://crypo.bz.ms/encryptors) - Best encryption for network security.Encrypt or Decrypt sensitive data using AES/DES/RCA encryptors (security tools).
 - [Cryptolab](http://manansingh.github.io/Cryptolab-Offline/cryptolab.html) - is a set of cryptography related tools.
 - [CrypTool](http://www.cryptool-online.org/) - Great variety of ciphers, encryption methods and analysis tools are introduced, often together with illustrated examples.
 - [keybase.io](https://keybase.io/) - Keybase maps your identity to your public keys, and vice versa.
@@ -344,6 +343,7 @@ encryption library providing MD5, SHA1, SHA2 hashing and HMAC functionality, as
 ### Web-sites
 
 - [Cryptography Stackexchange](http://crypto.stackexchange.com/) - Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography.
+- [Cryptopals Crypto Challenges](http://cryptopals.com/) - A series of applied cryptography challenges, starting from very basic challenges, such as hex to base 64 challanges, and gradually increasing the difficulty up to abstract algebra.
 - [Garykessler Crypto](http://www.garykessler.net/library/crypto.html) - An Overview of Cryptography.
 - [IACR](https://www.iacr.org/) - The International Association for Cryptologic Research is a non-profit scientific organization whose purpose is to further research in cryptology and related fields.
 - [Learn Cryptography](https://learncryptography.com/) - Dedicated to helping people understand how and why the cryptographic systems they use everyday without realizing work to secure and protect their privacy.