Add french book "Calcul mathématique avec Sage", collectif

remove broken macruby link

Formatting fixes:

Added empty line before heading "Information Retrieval" to fix html output.
Untabified one line in Python section.

Gradle Section + Building and Testing with Gradle

Added a Gradle Section and the book Building and Testing with Gradle

Fixing and Adding various links

une introduction aux makefile

Knockout mix-up

Added Ruby and Perl section with come link and other links

Upgrading the Structure of files

Fix cliffnotes markdown link

R language & Enhancement

Update free-programming-books.md

Res: http://cran.r-project.org/other-docs.html

Added a link to "Models of Computation" by John E. Savage to the
"Theoretical Computer Science" category.

Update free-programming-books.md

Add Rook's Guide to C++ (crowdfunded book)