Cleanup jcryption.php

- use internal openssl functions
- populate $_POST/$_REQUEST variables with unecrypted data
- no global variable use for decryption
 Use window.crypto.getRandomValues where available to get
    cryptographically random key

    Label CryptoJS code with urls
Classify php jcryption.

Update examples.
Don't unset the encryption key for the _SESSION.

If unset bi-directional is broken.
No need for pbkdf2, just slows things down.

Secret AES key is plenty random w/o it.
Merge branch 'php-refactor' of https://github.com/j-c-m/jCryption into develop

Conflicts:
	jquery.jcryption.3.0.1.js
	php/jcryption.php

Also updated the example and bumped version
Merge branch 'release/3.1.0'