[MRG] More documentation minor fixes

A PR I plan to keep open while I am browsing the documentation and bumping into minor things that can be improved.
"guarantee the future" seems to win the google battle against "warrant the future". Also this [link](http://www.linguee.com/english-french/search?source=auto&query=%22garantir+le+futur%22) shows a few occurrences from the European parliament, which hopefully hires translators we can trust.

Otherwise the same link has something like "to (help) ensure the future" if you like it better.