Calculate the SHA256 hash of text input.
sha256.js
/*
* A JavaScript implementation of the Secure Hash Algorithm, SHA-256,
* in FIPS 180-2
* Version 2.2 Copyright Angel Marin, Paul Johnston 2000 - 2009.
* Other contributers: Greg Holt, Andrew Kepert, Ydnar, Lostinet
* Distributed under the BSD License
* See http://pajhome.org.uk/crypt/md5 for details.
* Also http://anmar.eu.org/projects/jssha2
*/