Add margin to gallery to enhance display

[pled]

Hi,
This is a suggestion that in my opinion would make gallery display a bit nicer.
As of today, images are displayed full width, with no margin on right and left regarding to the "main full-width" class.
It looks like this :

I believe it would be nicer by adding a small margin on both sides, like below :

Note that it has an impact on the following remark : "There should be two spaces between the images to ensure they stay in the same line in Markdown" from the "Image gallery" example post. Ideally, margin should only be added on the left of first image, and on the right of last image ? It should be possible I guess.

Thank you for your wonderful theme.