Adding books about Backbone, AngularJS, GIT
Merge pull request #70 from haraldschilly/master

adding two link for "Sage", the mathematical software system
Added Scala School by Twitter
Merge pull request #73 from Xelom/patch-1

Added Scala School by Twitter
Update
Reordering, removing a non-free book
Added Natural Language Processing for the Working Programmer
Added 'Haskell and Yesod'
add theory section (vs algorithms or misc), seed with network theory book
Add Flask tutorail
fix url
fix url
fixed Perl 6 link in contents
Merge pull request #76 from Haskmell/yesod

Added 'Haskell and Yesod'
Merge pull request #81 from thekarangoel/patch-1

Add Flask tutorail
Merge pull request #82 from srayuws/master

fix url
Merge pull request #83 from OpossumPetya/patch-1

fixed Perl 6 link in contents
Merge branch 'natural_language' of github.com:Haskmell/free-programming-books into Haskmell-natural_language

Conflicts:
	free-programming-books.md
Professional Assembly Language book
racket guide