Fix image width

On mobile phones, images did not display very well because their
dimensions were hard-coded. Now the width is set to be maximum 100% of
the page width. This should fix the problem. @gpetit
Merge pull request #89 from agouge/fix-image-width

Fix image width

On mobile phones, images did not display very well because their
dimensions were hard-coded. Now the width is set to be maximum 100% of
the page width. This should fix the problem.