Formatting fixes:
Added empty line before heading "Information Retrieval" to fix html output.
Untabified one line in Python section.
remove broken macruby link
Merge pull request #445 from shelleyvadams/master

Formatting fixes:
Merge pull request #446 from eellson/remove-dead-link

remove broken macruby link
Berkeley link doesn't require signup
Add french book "Calcul mathématique avec Sage", collectif
Merge pull request #450 from ericguirbal/fr

Add french book "Calcul mathématique avec Sage", collectif
Merge pull request #448 from hiisi13/master

Algorithms - Berkeley link doesn't require signup