Included open sourced books from underscore.io (#2382)

* Included open sourced books from underscore.io

as per http://underscore.io/blog/posts/2017/05/29/why-we-open-sourced-our-books.html list of this books are open sourced:
Essential Scala
Learn to write robust, performant, idiomatic Scala. A focused guide for established developers.
Advanced Scala with Cats
Dive deep into functional patterns using Scala and Cats. For experienced Scala developers.
The Type Astronaut's Guide to Shapeless
Scrap your boilerplate and derive type classes with shapeless. For experienced Scala developers.
Essential Play
Learn to use the Play web framework to build web sites and services. For new to intermediate Scala developers.
The Lift Cookbook
Learn to use the Lift web framework to build web sites and services. For new to intermediate Scala developers.
Creative Scala
Learn functional programming with pictures! A fun and practical introduction for new developers.

* Included open sourced books from underscore.io alfabetically ordered

* Included open sourced books from underscore.io - addition of - Just fill the fields with any values

free-programming-books.md

@@ -2070,9 +2070,12 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 ### Scala
 
 * [A Scala Tutorial for Java programmers](http://www.scala-lang.org/docu/files/ScalaTutorial.pdf) (PDF)
+* [Advanced Scala with Cats](http://underscore.io/books/advanced-scala/) - Noel Welsh and Dave Gurnell (PDF, HTML, EPUB) *(Just fill the fields with any values)*
 * [Another tour of Scala](http://naildrivin5.com/scalatour/)
+* [Creative Scala](http://underscore.io/books/creative-scala/) - Noel Welsh and Dave Gurnell (PDF, HTML, EPUB) *(Just fill the fields with any values)*
 * [EAI Patterns with Actor Model](https://github.com/alexanderfefelov/eai-patterns-with-actor-model) - Vaughn Vernon
 * [Effective Scala](https://twitter.github.io/effectivescala/)
+* [Essential Scala](http://underscore.io/books/essential-scala/) - Noel Welsh and Dave Gurnell (PDF, HTML, EPUB) *(Just fill the fields with any values)*
 * [Learning Scala in small bites](http://matt.might.net/articles/learning-scala-in-small-bites/)
 * [Learning Scalaz](http://eed3si9n.com/learning-scalaz/)
 * [Pro Scala: Monadic Design Patterns for the Web](https://github.com/leithaus/XTrace/tree/monadic/src/main/book/content/)
@@ -2089,6 +2092,7 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 * [Scala Tutorial](http://www.tutorialspoint.com/scala/scala_tutorial.pdf) (PDF)
 * [tetrix in Scala](http://eed3si9n.com/tetrix-in-scala-html5-book)
 * [The Neophyte's Guide to Scala](http://danielwestheide.com/scala/neophytes.html) - Daniel Westheide
+* [The Type Astronaut's Guide to Shapeless](http://underscore.io/books/shapeless-guide/) - Dave Gurnell (PDF, HTML, EPUB) *(Just fill the fields with any values)*
 * [Xtrace](https://github.com/leithaus/XTrace/tree/monadic/src/main/book/content/)
 
 
@@ -2102,6 +2106,7 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 
 #### Play Scala
 
+* [Essential Play](http://underscore.io/books/essential-play/) - Dave Gurnell (PDF, HTML, EPUB) *(Just fill the fields with any values)*
 * [Play Framework Recipes](http://alvinalexander.com/scala/scala-cookbook-play-framework-recipes-pdf-ebook) - Alvin Alexander