Added Machine Learning Books
Added subcategory for Backbone.js and a link for 'Developing Backbone.js Applications'

Also alphabetized the subcategories under Javascript, now that there are three.
Update free-programming-books.md
Adding books about Backbone, AngularJS, GIT
Split C / C++ in two
Fix index
Add IDL guide.

IDL is language used on astronomy, but it is now being replaced by
Python. I have added here the Getting Started with IDL.
Added python books
Remove broken link for F# Survival Guide
Add "The Art of Assembly Language Programming" book.

Adding "The Art of Assembly Language Programming" by Randall Hyde
Add a guide to IDL.
Merge pull request #94 from gabraganca/IDL

Add IDL guide.
Merge pull request #95 from jdu/patch-1

Added python books
Merge pull request #96 from simoraman/master

Remove broken link for F# Survival Guide
Merge pull request #97 from matematikaadit/patch-1

Add "The Art of Assembly Language Programming" book.
Merge pull request #89 from JIghtuse/master

Few books from hackershelf.com
Added (Programming in D) book
Fix DTrace link
Added OpenSCAD User Manual
Add "Git Magic" book.