Bitcoin and cryptocurrency book from Princeton (#2375)

* added Solidity

* added Solidity

* added Solidity

* bitcoin book added

* fixed ordering on bitcoin book entry

* added authors for bitcoin and solidity books

* added Bitcoin and cryptocurrency Princeton book

free-programming-books.md

@@ -454,6 +454,7 @@
 * [Ansible Up & Running (first three chapters)](https://www.ansible.com/blog/free-ansible-book) *(account required)*
 * [Asterisk™: The Definitive Guide](http://solmu.org/pub/help/Asterisk/3nd_Edition_for_Asterisk_1.8)
 * [Barcode Overview](http://www.tec-it.com/download/PDF/Barcode_Reference_EN.pdf) (PDF)
+* [Bitcoin and Cryptocurrency Technologies](https://d28rh4a8wq0iu5.cloudfront.net/bitcointech/readings/princeton_bitcoin_book.pdf) -  Arvind Narayanan, Joseph Bonneau, Edward Felten, Andrew Miller, Steven Goldfeder (PDF)
 * [Come, Let's Play: Scenario-Based Programming Using Live Sequence Charts](http://www.wisdom.weizmann.ac.il/~playbook/)
 * [Communicating Sequential Processes](http://www.usingcsp.com/cspbook.pdf) - Tony Hoare (PDF)
 * [Computer Musings](http://scpd.stanford.edu/knuth/index.jsp) (lectures by Donald Knuth)