Removed {::nomarkdown}{:/} wrapping picturefill

- only tested on redcarpet markdown library
Tested changes from johnfmorton:patch-1 pull request on d26f72b under kramdown and maruku.
Fixed an issue where markdown converted 4-space indentation to code blocks using an escape sequence.
Merge pull request #31 from obxdesignworks/patch-fix-markdown-indentation

Patch: fix markdown indentation